Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.92.044702

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Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0139441

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Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevMaterials.7.024401

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

Reverse Monte Carlo (RMC) calculation was performed to visualize the atomic arrangement in a disordered Fe55Ni45 alloy, which is classified as an intermediate structure between the non-crystalline glass and crystalline structures. The optimized structure of the ferromagnetic phase at low pressures revealed that Fe and Ni atoms were displaced from a perfect fcc lattice to elongate the nearest neighboring Fe-Fe atomic pairs, therefore, Fe-Fe atomic pairs have longer bond length than Fe-Ni and Ni-Ni atomic pairs. Because the elongation becomes negligible during the pressure-induced destabilization of the ferromagnetic state, the elongation of Fe-Fe pairs is the atomic scale origin of the volume expansion due to a large magnetovolume effect. Compared with the atomic arrangement in the Fe65Ni35 Invar alloy, a relationship between Fe-Fe atomic pairs, the Invar effect and elastic anomalies in the compression curve is elucidated.

DOI： 10.3389/fmats.2022.954110

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report our investigations on the effects of pressure on the electronic and magnetic properties of magnetic Dirac semimetal EuMnBi2 by using electrical transport, synchrotron x-ray diffraction, and x-ray absorption spectroscopy. The antiferromagnetic interaction due to the Eu magnetic moment in EuMnBi2 is enhanced under pressure up to similar to 3.9GPa. The Neel temperature (T-N) is found to disappear above 4 GPa and a new transition T-t at around 29 K emerges above 6 GPa. T-t remains relatively constant up to 15 GPa, above which it increases with further compression, reaching similar to 60K at 22 GPa. Eu L-edge x-ray absorption spectroscopy revealed a valence change of Eu toward a trivalent state that begins above 6 GPa, which indicates that T-t is likely related to the valence transition temperature of Eu. Sign reversal of the Hall resistivity above 7 GPa suggests that the valence change of Eu also induces a Fermi surface modification.

DOI： 10.1103/PhysRevResearch.3.043028

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Publishing type：Research paper (scientific journal)  

In this study, atomic-scale origin of the Invar effect, which is nearly-zero thermal expansion observed in the Invar alloy Fe65Ni35, was investigated by reverse Monte Carlo analysis using complementary data sets of extended x-ray absorption fine structure and x-ray diffraction. The interatomic distances of the nearest neighboring Fe-Fe atomic pairs were ∼0.02 Å longer than those of the Fe-Ni and Ni-Ni pairs at the minimum pressure in this study (0.6 GPa). The elongation in the Fe-Fe pairs was suppressed with increasing pressure, and the distances of the three pairs were comparable under pressures above the magnetic transition from ferromagnetic to paramagnetic phase at Pc≈7 GPa. Therefore, the Fe-Fe pairs dominantly contribute to the volume expansion due to the magnetovolume effect. Because a similar magnitude of elongation was observed in the Fe-Fe pairs of a non-Invar Fe-Ni alloy, we conclude that the Invar effect originates from the delicate balance between the number of Fe-Fe pairs and their elongation depending on the magnetization.

DOI： 10.1103/PhysRevB.103.L220102

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The alpha (bcc) phase of single-crystalline iron was compressed along the [111](alpha) direction under quasihydrostatic and nonhydrostatic conditions. The emergence of the epsilon (hcp) phase variants via the pressure-induced martensitic transformation was investigated using x-ray diffraction and optical observations of the sample surface. In quasihydrostatic compression, the alpha-epsilon transition occurred at approximately 14 GPa accompanied by the sudden appearance of texture structures on the mirror-polished sample surface. The texture structure divided the sample surface into two characteristic regions: distorted regions with undulations and flat regions without undulations. Although martensitic transformation based on the Burgers model allows for the emergence of 12 epsilon variants from one single-crystalline phase, the transition proceeded according to the Burgers model, but selected variants preferably emerged depending on the regions in the texture structure. The flat region consisted of only three variants whose c axes were parallel to the sample surface. The region near the undulation exhibited a large number of variants whose c axes aligned parallel and nonparallel to the sample surface. The alpha-epsilon transition under nonhydrostatic compression deviated from the Burgers model, and the variant selection was not observed. This study demonstrates that the quasihydrostatic compression along [111](alpha) reduces the number of variants via strong variant selection. The strong preferred orientation is useful for investigating the anisotropy of physical properties in the epsilon phase.

DOI： 10.1103/PhysRevB.102.054106

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union ({AGU})  

DOI： 10.1029/2020GL088169

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Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.30.011172

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Language：English   Publishing type：Research paper (scientific journal)  

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. We present the first application of double-stage diamond anvil cells (ds-DACs) to X-ray absorption spectroscopy (XAS) of Rhenium (Re) metal. By using highly stable and sub-micron sized X-ray beam, XAS spectra were successfully observed at the (Formula presented.) -edges from the sample encapsulated in the small space between the second-stage anvils. The pressure generation exceeding 300 GPa was evaluated by the pressure-induced shift of extended X-ray absorption fine structure (EXAFS) oscillation at the (Formula presented.) -edge. The profile of white-line at the (Formula presented.) -edges broadened with increasing pressure, which indicates the modification of the Re (Formula presented.) band structure. The present results demonstrate the high ability of XAS technique combined with ds-DACs as a probe for crystal structure and electronic structure under ultrahigh pressure.

DOI： 10.1080/08957959.2019.1702174

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Both micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micron beam and the conically supported 2nd stage anvils (micro-anvils) with 10 mu m culet enable us to obtain good quality X-ray diffraction peaks from the sample at around 400 GPa. The relationship between confining pressure and sample pressure depends heavily on the initial height (thickness) of micro-anvils, the difference of a few micrometers leads to a quite different compression path. The conical support type is a solution to retain both enough thickness and strength of micro-anvils at higher confining pressure conditions. All conical support ds-DAC experiments terminated by the failure of the 1st stage anvil instead of 2nd one. The combination of ultra-fine NPD 2nd stage anvil and NPD 1st stage anvil opens a new frontier for measurement of the X-ray absorption spectrum above 300 GPa.

DOI： 10.1080/08957959.2019.1691190

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/JPSJ.88.114601

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Publishing type：Research paper (scientific journal)  

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. We present the element-selective local structure analysis of ferromagnetic Fe65 Ni35 Invar alloy and Fe72 Pt28 alloy under high pressures as a recent application of nano-polycrystalline diamond (NPD) to extended X-ray absorption fine structure (EXAFS). The Invar effect is a phenomenon where thermal expansion becomes nearly zero in a wide range of temperatures. Fe72 Pt28 is an alloy exhibiting negative thermal expansion. Our EXAFS analysis successfully revealed significant differences in element-selective elastic properties between local structures around Fe and Ni/Pt. The local structure around Fe has a smaller bulk modulus than that of Ni. Hence, the more compressive behavior around Fe is responsible for the anomalously soft elastic property that is characteristic of Invar alloy. In the case of Fe72 Pt28, Fe has a smaller bulk modulus than Pt; however, the difference in bulk modulus in the ferromagnetic phase is small compared with that of Invar alloy. We also report different trends of pressure-induced decrease in Debye-Waller factors toward paramagnetic phases.

DOI： 10.1080/08957959.2019.1702175

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

We report the results of the X-ray absorption spectroscopy (XAS) on the intermediate valence compound SmB6. The XAS measurements were performed near the nonmagnetic-magnetic phase boundary. Mean Sm valence vSm was estimated from absorption spectra, and we found that vSm near the boundary (P≥10GPa and T∼12K) is far below a trivalent state with magnetic characteristics. Although the result is markedly different from the cases of pressure induced magnetic orders in Yb and Ce compounds, it is likely that the large deviation from the trivalent state seems to be common in some Sm compounds which possess electronic configuration between 4f5 and 4f6 with multi 4f electrons.

DOI： 10.1016/j.physb.2017.09.053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

We have measured the X-ray absorption spectra (XAS), electrical resistivity and magnetic susceptibility of EuRh2Si2, which undergoes a valence transition under high pressures. A sharp decrease in the Eu valence determined from the XAS was observed at around 70 K in the temperature dependence at P = 1.2–1.9 GPa. In the temperature dependence of electrical resistivity and magnetic susceptibility, we observed jumps associated with the temperature-induced valence transition under high pressures. The magnetoresistance detected a field-induced valence transition. The results are discussed from the thermodynamic point of view.

DOI： 10.1016/j.physb.2017.10.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We report a systematic study of Sm valence in the prototypical intermediate valence compound SmB6. Sm mean valence vSm was measured by x-ray absorption spectroscopy as a function of pressure (1&lt
P&lt
13GPa) and temperature (3&lt
T&lt
300K). Pressure-induced magnetic order was detected above Pc=10GPa by resistivity measurements. A shift toward the localized 4f state with increasing P and/or T is evident from an increase in vSm. However vSm at Pc is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the T dependence of vSm(P,T), we found that vSm(P,T) consists of two different characteristic components: One is associated with low-energy electronic correlations involving Kondo-like behavior, and the other is associated with high-energy valence fluctuations.

DOI： 10.1103/PhysRevB.97.161116

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1361-648x/aaaca3

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Other Link： http://iopscience.iop.org/article/10.1088/1361-648X/aaaca3/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The effect of Fe-site substitution on structural and physical properties of the infinite layer iron oxide SrFeO2 was investigated under high pressure by Fe-57 Mossbauer spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, Xray magnetic circular dichroism, and electrical resistance measurements using a diamond-anvil cell. Both 20% Mn-and Co-substituted samples exhibit spin transitions from a high-spin (S = 2) to an intermediate-spin (S = 1) state at P-c similar to 32 GPa, which is much the same pressure 33 GPa observed in SrFeO2. This result indicates that the spin transition pressure is insensitive to the d-orbital electron counts [Mn2+ (d(5)), Fe2+ (d(6)), Co2+ (d(7))], but is governed by the local structure around the Fe site.

DOI： 10.7566/JPSJ.86.124716

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

X-ray absorption spectra at the Ti K-edge of a SrTiO3 single crystal under uniaxial pressure were measured to obtain evidence of uniaxial pressure-induced polarization predicted in SrTiO3 from the electronic viewpoint. The pre-edge 3d-eg peak decreases in intensity with increasing uniaxial pressure, together with an energy shift to higher energy side. Contrary to uniaxial deformation, these changes were independent of incident x-ray polarization. This implies the presence of a mechanism that maintains the isotropic coordination environment around a Ti atom, i.e. a tilt and rotation of the TiO6 octahedron accompanied by its isotropic shrinkage, hence the local polarization essential to the ferroelectric order cannot be observed.

DOI： 10.1088/1361-648X/aa7ec6

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Publishing type：Research paper (international conference proceedings)  

© Published under licence by IOP Publishing Ltd. We have carried out the high-pressure measurement of X-ray absorption spectroscopy on the intermediate valence compound SmB6 which shows magnetic ordering as well as an insulator-metal transition at critical pressure Pc ∼ 10 GPa. The valence of Sm atom at room temperature increases with increasing pressure, however it is far below a trivalent state at Pc . In contrast to cases of pressure-induced nonmagnetic-magnetic transition in Yb compounds, which mostly occurs in the scheme of well localized 4f electrons, the present observation suggests that electronic system in SmB6 still possesses strong delocalized characters at Pc .

DOI： 10.1088/1742-6596/868/1/012008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

To understand how the constituent atoms participate in the hydrogenation of Pd-based alloys at similar to 0.1 MPa of hydrogen pressure (P-H2), we investigated the electronic states in Pd-M (M = Ru, Rh, Ag, and Au) alloys and their hydrides element-selectively by using x-ray absorption spectroscopy at the L-2,L-3 edges. Spectral changes near the absorption edge demonstrate that both Pd and M atoms form bonds with II atoms in the Pd-M (M = Ru and Rh) alloys even at P-H2 similar to 0.1 MPa. This is a striking result because high pressures of more than 1 GPa are required for the hydrogenation of Rh and Ru pure metals. In contrast, only Pd atoms bond with H atoms and the M-H bond is absent in the case of Pd-M (M = Ag and Au) alloys. Therefore, the hydrogen-induced changes in the electronic states differ between Ms with fully occupied d shells and Ms with partially occupied d shells. This study reveals that the thermodynamic hydrogenation properties of Pd-M alloys can be determined by a combination of the formation of the M-H bond and lattice expansion or compression by alloying Pd metal with M.

DOI： 10.1103/PhysRevB.95.024116

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have carried out the high-pressure measurement of X-ray absorption spectroscopy on the intermediate valence compound SmB6 which shows magnetic ordering as well as an insulator-metal transition at critical pressure P-c similar to 10 GPa. The valence of Sm atom at room temperature increases with increasing pressure, however it is far below a trivalent state at P-c. In contrast to cases of pressure-induced nonmagnetic-magnetic transition in Yb compounds, which mostly occurs in the scheme of well localized 4f electrons, the present observation suggests that electronic system in SmB6 still possesses strong delocalized characters at P-c.

DOI： 10.1088/1742-6596/868/1/012008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Fe-57-polarized synchrotron radiation Massbauer spectroscopy (PSRMS) with an X-ray phase plate and a nuclear Bragg monochromator was used to study ferrimagnetic GdFe2 in high-pressure hydrogen. The pressure-dependent spectra clearly showed a two-step magnetic transition of GdFe2. Fe-57-PSRMS with circular polarization gave direct evidence that the Fe moment was directed parallel to the net magnetization of the GdFe2 hydride at 20 GPa. This spin configuration was opposite to that of the initial GdFe2, suggesting an extreme weakening of the antiferromagnetic interaction between Fe and Gd. Fe-57-PSRMS enables the characterization of the nonuniform properties of iron-based polycrystalline powder alloys. The excellent applicability of Fe-57-PSRMS covers a wide range of scientific fields.

DOI： 10.7566/JPSJ.85.123707

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

In strongly correlated electron systems, a fundamental understanding of the quantum critical behavior in the vicinity of a magnetic quantum critical point (QCP) remains one of the important issues for decades. In particular, the unconventional criticality, which cannot be explained by the spin fluctuation theory, has attracted much attention in 4f electron systems, and the role of the valence instability has been discussed both from theoretical and experimental points of view. Here, we present our systematic high pressure study of X-ray absorption spectra on YbNi3Ga9 and EuFe2As2, revealing the characteristic pressureinduced valence crossover and possibly the relevance of the valence instability to the physical properties near the magnetic QCP.

DOI： 10.1080/08957959.2016.1199695

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Language：English   Publisher：TAYLOR & FRANCIS LTD  

DOI： 10.1080/08957959.2016.1215820

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Publishing type：Research paper (scientific journal)  

© 2016 Informa UK Limited, trading as Taylor & Francis Group. Recently, nano-polycrystalline diamond (NPD) anvils have been widely applied in high pressure research using X-ray absorption spectroscopy (XAS). The nanometer-sized polycrystallization in NPD anvils enables us to obtain glitch-free X-ray absorption spectra. This advantage of NPD anvils drastically improves the experimental conditions of XAS, which has previously used conventional single-crystal diamond (SCD) anvils. Distorted spectra due to the glitches from the SCD anvils have been an inevitable problem of XAS. This paper reviews recent studies of XAS and related spectroscopic techniques using the NPD anvils, which have mainly been performed on BL39XU of SPring-8. We demonstrate how NPD anvils are useful when using XAS for high pressure research.

DOI： 10.1080/08957959.2016.1205048

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The electronic properties of a perovskite Fe4+ oxide, CaCu3Fe4O12, pressurized in a diamond anvil cell at pressures up to 50 GPa, were investigated by X-ray diffraction, electrical resistance measurements, X-ray absorption spectroscopy, and Fe-57 Mossbauer spectroscopy. The first transformation from a charge-disproportionated (Fe3+ and Fe5+) semiconducting high-spin state to an approximately charge-uniform (Fe(4-delta)+ and Fe(4+delta)+) metallic high-spin state occurred at similar to 15 GPa. This was followed by a second transformation to a completely charge-uniform (Fe4+) metallic low-spin state at similar to 30 GPa. This is the first observation of pressure-induced two-step suppression of charge disproportionation in perovskite iron oxides.

DOI： 10.7566/JPSJ.85.034716

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Language：English   Publishing type：Research paper (scientific journal)  

We report a novel pressure-driven spin crossover in layered cobalt oxyfluoride Sr2CoO3F with a distorted CoO5 square pyramid loosely bound with a fluoride ion. Upon increasing pressure, the spin state of the Co(III) cation gradually changes from a high spin state (S = 2) to a low spin state (S = 0) accompanied by a anomalously large volume contraction (bulk modulus, 76.8(5) GPa). The spin state change occurs on the CoO5 pyramid in a wide pressure range, but the concomitant gradual shrinkage of the Co-F bond length with pressure gives rise to a polyhedral transformation to the CoO5F octahedron without a structural phase transition, leading to the full conversion to the LS state at 12 GPa. The present results provide new effective strategy to fine-tune electronic properties of mixed anion systems by controlling the covalency in metal-ligand bonds under pressure.

DOI： 10.1038/srep36253

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The local structures around Co and Fe in BiCo1-xFexO3 (BCFO) have been determined element-selectively by means of extended x-ray absorption fine structure (EXAFS) measurements at the Co and Fe K edges. In the tetragonal (T) phase at x <= 0.63, both Fe and Co ions are trivalent and locate in the O-5 pyramidal coordination. The four in-plane Fe bonds with transverse oxygen (Fe-O2) split into 2 x 2 bonds in the monoclinic (M) phase at 0.63 <= x <= 0.73 whereas the Co-O2 bonds do not show a split exceeding the resolution of our EXAFS analysis. This result is an element-specific interpretation of the polarization rotation in the M phase around the morphotropic phase boundary. The components of thermal vibration and static disorder are evaluated separately from the temperature dependence of the Debye Waller factor from T = 8 K to 300 K. The static disorder of the Fe site is large compared to that of the Co site, thereby indicating that Fe is unstable in the O-5 pyramidal coordination of the T and M phases. This study demonstrates that the instability of Fe ions plays an important role in the sequential structural distortion of the BCFO system.

DOI： 10.1103/PhysRevB.92.054108

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN PHYSICAL SOC  

X-ray absorption spectra under uniaxial pressure were measured at the Ti K-edge of a SrTiO3 single crystal in order to obtain direct evidence for the ferroelectric transition that is expected on the basis of second harmonic generation studies. A uniaxial pressure was applied perpendicular to the ab-plane. The pre-edge peak, which corresponds to Ti 3d e (g) -O 2p sigma bonding, shows little change across the transition temperature of 40 K at 1 GPa. This indicates that a local electric dipole moment is not induced under uniaxial pressure, as opposed to the macroscopic ferroelectric moments that are predicted to be induced along the ab-plane.

DOI： 10.3938/jkps.66.1386

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence YbNi3Ga9 under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below P-c similar to 9 GPa where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

DOI： 10.1103/PhysRevLett.114.086401

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Language：Japanese  

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_1254

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_2497

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_2080

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_2409

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2147

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2160

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2173

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Language：English   Publishing type：Research paper (international conference proceedings)  

A heavy-fermion antiferromagnet Ce2NiGa12 has been studied at a viewpoint of pressure effects. Electrical resistivity measurements show that the antiferromagnetic ordering is suppressed at PC ∼ 5.5 GPa, and that Fermi liquid behaviour is observed above PC. To investigate how Ce valence state is associated with the observed critical phenomena, X-ray absorption spectra at Ce L3-edge have been performed. Ce valence state drastically varies at Pv ∼ 9 GPa in the initial applying pressure process, whereas anomalous behaviour is not observed in the Ce valence under pressures around PC. Consequently, the quantum critical phenomena in Ce2NiGa12 around PC is not strongly connected with Ce valence state.

DOI： 10.1088/1742-6596/568/4/042015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We have carefully investigated the α-ε transition pathway of iron under quasihydrostatic pressures. For this purpose, combined measurements of extended x-ray absorption fine structure (EXAFS) and x-ray magnetic circular dichroism at the Fe K edge were performed using a helium pressure-transmitting medium. Collapse of the ferromagnetism simultaneously occurs with the α-ε structural transition, which is in contrast to the scenario that the transition is driven by the pressure-induced instability of the ferromagnetism in α phase of iron. We conclude that shear stress is important to initiate the α-ε transition. Our model to fit the EXAFS profile demonstrates that the local atomic arrangement in ε phase is slightly distorted due to unfinished shuffle motion, whereas shear motion finishes at the beginning of the transition. © 2014 American Physical Society.

DOI： 10.1103/PhysRevB.90.014422

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have carefully investigated the alpha-epsilon transition pathway of iron under quasihydrostatic pressures. For this purpose, combined measurements of extended x-ray absorption fine structure (EXAFS) and x-ray magnetic circular dichroism at the Fe K edge were performed using a helium pressure-transmitting medium. Collapse of the ferromagnetism simultaneously occurs with the alpha-epsilon structural transition, which is in contrast to the scenario that the transition is driven by the pressure-induced instability of the ferromagnetism in a phase of iron. We conclude that shear stress is important to initiate the alpha-epsilon transition. Our model to fit the EXAFS profile demonstrates that the local atomic arrangement in epsilon phase is slightly distorted due to unfinished shuffle motion, whereas shear motion finishes at the beginning of the transition.

DOI： 10.1103/PhysRevB.90.014422

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

To understand the hard magnetism of L1(0)-type ordered FeNi alloy, we extracted the L1(0)-FeNi phase from a natural meteorite, and evaluated its fundamental solid-state properties: sample composition, magnetic hysteresis, crystal structure and electronic structure. We executed multidirectional analyses using scanning electron microscopy with an electron probe micro-analyzer (SEM-EPMA), a superconducting quantum interference device (SQUID), x-ray diffraction (XRD) and magnetic circular dichroism (MCD). As a result, we found that the composition was Fe: 50 : 47 +/- 1 : 98 at.%, Ni: 49 : 60 +/- 1 : 49 at.%, and an obvious superlattice peak is confirmed. The estimated degree of order was 0.608, with lattice constants a = b = 3 : 582 angstrom and c = 3 : 607 angstrom. The obtained coercivity was more than 500 Oe. MCD analysis using the K absorption edge suggests that the magnetic anisotropy could originate from the orbital magnetic moment of 3d electrons in Fe; this result is consistent with that in a previous report obtained with synthetic L1(0)-FeNi.

DOI： 10.1088/0953-8984/26/6/064206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have performed X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) measurements at pressures up to 17 GPa for the clathrate Eu8Ga16Ge30 (Curie temperature T-C = 36 K). The temperature dependence of the XMCD spectra agrees well with that of the DC magnetization at ambient pressure. The TC is gradually enhanced with increasing pressures up to 13.3 GPa, and the divalent state of the Eu ions with J = 7/2 remains stable, but at 17 GPa the XMCD intensity is strongly suppressed and a spectral weight corresponding to the trivalent state of Eu ions (with no magnetic moment) appears in the XAS spectrum. The concurrent change from the type-I clathrate structure to an amorphous phase has been observed by X-ray diffraction experiment. We conclude that the amorphization of this compound induces the mixed valence state, which collapses the ferromagnetism.

DOI： 10.7566/JPSJ.83.013701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

For the unconventional heavy fermion compound SmOs4Sb12, the temperature dependence of the Sm valence state was investigated by Sm L-m-edge X-ray absorption spectroscopy under the application of pressure. The Sm valence was found to fluctuate up to a pressure of 3.5 GPa. From the pressure and temperature dependence of the average Sm valence, it was concluded that the Sm divalent contribution plays an important role in the heavy fermion behavior of SmOs4Sb12. Pressure dependence of a characteristic temperature in the Sm valence states exhibits a minimum at around 1 GPa. This finding demonstrates the correlation between the Sm valence and heavy fermion behavior in SmOs4Sb12.

DOI： 10.7566/JPSJ.82.023707

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Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Hydrogen-induced modification of electronic structures, magnetic states, and crystal structures of transition metal (TM=Fe, Co, and Ni) monohydrides was investigated using TM K-edge x-ray magnetic circular dichroism (XMCD), x-ray diffraction, and first-principles calculations. The TM hydrides undergo narrowing of TM 3d density of states (DOS) and significant shifts in the Fermi energy E F due to hydrogenation, which is responsible for the magnetic properties of the TM hydrides: ferromagnetic FeH, ferromagnetic CoH, and paramagnetic NiH. The reconstruction of the electronic structure is mainly attributed to the appearance of bonding and antibonding states together with hydrogen-induced volume expansion. We demonstrate that the characteristic XMCD profile of the TM hydrides near the absorption edge probed the reconstruction of the electronic structure above E F. The pressure dependence of XMCD revealed that the ferromagnetic state of FeH is less stable than that of CoH under pressure. The different hydrogenation processes between CoH and NiH at room temperature are reported by means of x-ray diffraction. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.86.104430

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

Nano-polycrystalline diamond (NPD) [Irifune et al. (2003), Nature (London), 421, 599] has been used to obtain a glitch-free X-ray absorption spectrum under high pressure. In the case of conventional single-crystal diamond (SCD) anvils, glitches owing to Bragg diffraction from the anvils are superimposed on X-ray absorption spectra. The glitch has long been a serious problem for high-pressure research activities using X-ray spectroscopy because of the difficulties of its complete removal. It is demonstrated that NPD is one of the best candidate materials to overcome this problem. Here a glitch-free absorption spectrum using the NPD anvils over a wide energy range is shown. The advantage and capability of NPD anvils is discussed by a comparison of the glitch map with that of SCD anvils.

DOI： 10.1107/S0909049512026088

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Nano-polycrystalline diamond (NPD) [Irifune et al. (2003), Nature (London), 421, 599] has been used to obtain a glitch-free X-ray absorption spectrum under high pressure. In the case of conventional single-crystal diamond (SCD) anvils, glitches owing to Bragg diffraction from the anvils are superimposed on X-ray absorption spectra. The glitch has long been a serious problem for high-pressure research activities using X-ray spectroscopy because of the difficulties of its complete removal. It is demonstrated that NPD is one of the best candidate materials to overcome this problem. Here a glitch-free absorption spectrum using the NPD anvils over a wide energy range is shown. The advantage and capability of NPD anvils is discussed by a comparison of the glitch map with that of SCD anvils. © 2012 International Union of Crystallography Printed in Singapore - all rights reserved.

DOI： 10.1107/S0909049512026088

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The magnetic EXAFS technique was applied to study the local magnetic structure in Fe-Ni Invar alloy under high pressures. Nano-polycrystalline diamond was used to apply pressure in a diamond anvil cell. As a result, we succeeded in recording a glitch-free spectrum with a high accuracy by preventing Bragg diffraction from the diamonds. As the pressure was increased, the ferromagnetic correlation was strongly reduced, which was more remarkable for Fe atoms than for Ni atoms. The canting effect of the magnetic moment may be crucial for a rapid decrease in the ferromagnetic correlation. This local magnetic structure in the Invar alloy is consistent with a model based on the non-collinear spin structure.

DOI： 10.1088/1742-6596/377/1/012039

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Magnetic states of Fe, Co, and Ni hydrides under pressure have been investigated by X-ray magnetic circular dichroism (XMCD) at the K-edge. At room temperature, Fe, Co, and Ni metals are hydrogenated to ferromagnetic FeH, ferromagnetic CoH, and paramagnetic NiH, respectively. A sharp XMCD profile is observed after hydrogenation, which is attributed to the hydrogen-induced reconstruction of the electronic structure. The pressure dependence of XMCD demonstrates that the ferromagnetic state of FeH is less stable than that of CoH under pressure.

DOI： 10.1088/1742-6596/377/1/012041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Magnetic Compton scattering at high pressure is presented for the first time. To study the pressure-induced magnetic transition in Laves-phase ErCo2, Er 4f and Co 3d spin magnetic moments, together with the conduction electron component, were separately and quantitatively estimated at pressures up to 1.84 GPa. The Co 3d spin moments show a remarkable reduction with increasing pressure, which is in contrast to the weak pressure variation of the Er 4f spin moment. The relationship between the magnetic transition and instability of the Co 3d moment at high pressure is discussed from the viewpoint of lattice contraction and the molecular field of Er 4f moments.

DOI： 10.1143/JPSJ.80.093705

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

X-ray magnetic circular dichroism (XMCD) study of 3<i>d</i> transition metal hydrides FeH, CoH, and NiH is presented. The hydrogen effects on the electronic structure and magnetic states have been investigated. This study reveals that ferromagnetic Ni transforms to nonmagnetic NiH, whereas FeH and CoH remain ferromagnetic after the hydrogenation. The XMCD profiles indicate that the electronic states of 3<i>d</i> electron near the Fermi energy are modified as a result of the hydrogenation. In this article, the stability of the ferromagnetic state in FeH and CoH is also discussed.<br>

DOI： 10.4131/jshpreview.21.176

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Other Link： https://jlc.jst.go.jp/DN/JALC/00380186172?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IBM CORP  

The local structure of an iron meteorite was analyzed using photoemission electron microscopy (PEEM) and hard x-rays. The x-ray absorption fine-structure spectrum was obtained for each pixel in the PEEM image. The spectrum provides a wide variety of information, e. g., chemical composition, electronic structure, and lattice structure, in the interface region of the Widmanstatten structure. The shape of the absorption edge and the radial distribution function indicate that the structural phase changes from body-to face-centered cubic phases as the Ni composition at the interface is increased. The use of PEEM and hard x-rays is an attractive approach for local structure analysis.

DOI： 10.1147/JRD.2011.2159159

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We present the results of electrical resistivity, ac specific heat, magnetic susceptibility, x-ray absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under pressure. Applying pressure leads to a continuous suppression of the antiferromagnetism associated with Fe moments and the antiferromagnetic transition temperature becomes zero in the vicinity of a critical pressure P-c similar to 2.5-2.7 GPa. Pressure-induced reentrant superconductivity, which is highly sensitive to the homogeneity of the pressure, only appears in the narrow pressure region in the vicinity of P-c due to the competition between superconductivity and the antiferromagnetic ordering of Eu2+ moments. The antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state above 6 GPa. We also found that the ferromagnetic order is suppressed with further increasing pressure, which is connected with a valence change of Eu ions.

DOI： 10.1103/PhysRevB.84.024502

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion &lt; -10(-4) K-1 over a temperature range similar to 100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low-and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi0.95La0.05NiO3 is -137x10(-6) K-1 and a value of -82x10(-6) K-1 is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders.

DOI： 10.1038/ncomms1361

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We present direct observation of the magnetic state in a beta(fcc)-Co high-pressure phase accompanied by the epsilon -&gt;beta (hcp -&gt; fcc) transition by means of Co K-edge x-ray magnetic circular dichroism up to 170 GPa. In contrast to the prediction made in previous studies that beta(fcc)-Co is nonmagnetic, this study concludes that beta(fcc)-Co is paramagnetic with anomalously large magnetic susceptibility chi = 1.5(4) x 10(-3) cm(3)/g.

DOI： 10.1103/PhysRevB.83.180409

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

To examine theoretical models of the Invar effect, X-ray magnetic circular dichroism and magnetic extended X-ray absorption fine structure (MEXAFS) measurements are performed under high pressures at the Fe and Ni K-edges in 35.4at.% Ni-Fe alloy. An oscillatory MEXAFS signal is observed up to 6 GPa. Its amplitude significantly decreases with increasing pressure. The magnetic component of the radial distribution function, obtained by taking the Fourier transform, shows a different reduction in the ferromagnetic correlations of Fe and Ni absorbing atoms. The present results are favorable to the noncollinear spin structure picture rather than the Fe 2 gamma-state model.

DOI： 10.1143/JPSJ.80.023709

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The structural and electronic properties of BiCoO3 under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO3 type to a centrosymmetric GdFeO3 type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co3+ is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure temperature phase diagram of BiCoO3 has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.

DOI： 10.1021/ja102987d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The electronic band Structure of ordered FePt3(110) single crystal was studied by angle-resolved photoemission spectroscopy with synchrotron radiation. The energy band dispersions along the X-Gamma-X and R-M-R directions of a simple cubic Brillouin zone were Successfully observed at room temperature.,g file latter direction, band folding due to antiferromagnetic (AF) ordering was clearly observed Along the latter direction, band folding due to antiferromagnetic (AF) ordering was clearly observed below the Neel temperature (T-N2) of 100 K. Through comparison with theoretical Calculations. (1/2, 0, 0)-type AF ordering or a mixture of the (1/2, 0, 0)-type and (1/2, 1/2, 0)-type AF orderings was concluded to occur below T-N2. These magnetic orderings can be understood from the viewpoint of the nesting between the electron and hole pockets.

DOI： 10.1143/JPSJ.79.024703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Photoelectron emission microscopy has been carried out to study the magnetic properties of iron meteorite associated with the Widmanstatten structure for the first time. A magnetic circular dichroic image reveals a unique magnetic domain structure, resulting in the "head-on&apos;&apos; magnetic coupling over the interface between the alpha and gamma lamellae. Such a magnetic domain structure is unfavorable in any synthetic Fe-Ni alloys. Micromagnetics simulation reasonably explains that the formation of magnetic domains is induced by the L1(0)-type FeNi (tetrataenite) phase segregated at the boundary in the Widmanstatten structure. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/APEX.3.013001

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Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press (Materials Research Society)  

DOI： 10.1557/proc-1262-w04-02

DOI： 10.1557/PROC-1262-W04-02

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Publishing type：Research paper (international conference proceedings)  

In order to study magnetic states in Fe-hydride under pressure, X-ray magnetic circular dichroism (XMCD) at the Fe K-edge has been measured up to 27.5 GPa. As a result, hydrogenation from bcc-Fe to dhcp-FeH occurs within a narrow region of 3.2-3.8 GPa, which is clearly observed by the dichroic profile in dhcp-FeH differing from that in bcc-Fe. Influence of H atoms on Fe 3d and 4p electronic states is discussed using the pressure-dependent XMCD and the first-principles calculation. © 2010 Materials Research Society.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

To investigate the change in the electronic structure of BiNiO3 accompanied by metal-insulator (MI) transition, we measured x-ray absorption spectroscopy (XAS) spectra at the Ni K and Bi L edges under various pressures up to 6 GPa. Both Bi L-3 and Ni K edge XAS spectra clearly change at 4 GPa, indicating the electronic state in Bi and Ni ion changes. A quantitative analysis of the Ni K edge spectra in the pre-edge region based on the charge-transfer cluster model including multiplet terms revealed that the electronic configuration changes from d(8) in the insulating phase to 56% d(7)+44% d(8)L_ in the metal phase. From these results, we concluded that the MI transition in BiNiO3 is induced by the collapse of charge-transfer gap and is governed by the redistribution of O 2p ligand holes.

DOI： 10.1103/PhysRevB.80.233104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

An X-ray magnetic circular dichroism experiment under multiple extreme conditions, 2 &lt;= T &lt;= 300 K, H &lt;= 10 T and P &lt;= 50 GPa, has been achieved at SPring-8 BL39XU. A combination of the high-brilliant X-ray beam and a helicity-controlled technique enabled the dichroic signal to be recorded with high accuracy. The performance is shown by the outcome of pressure-induced ferromagnetism in Mn(3)GaC and the pressure-suppressed Co moment in ErCo(2). Two technical developments, a tiny diamond anvil cell inserted into a superconducting magnet and in situ pressure calibration using 90 degrees Bragg diffraction from a NaCl marker, are also presented. X-ray magnetic spectroscopy under multiple extreme conditions is now opening a new approach to materials science.

DOI： 10.1107/S0909049509034700

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have measured x-ray magnetic circular dichroism spectra at the Co and Pt L-2,L-3-edges in Co80Pt20 perpendicular magnetization films, wherein the uniaxial magnetic anisotropy constant, K-u, significantly increases with decreasing film thickness, delta, and reaches 1.7x10(7) erg/cm(3) for delta=3 nm. The anisotropy of the orbital magnetic moment (AOM) was estimated as a function of delta, and the relationship between AOM and K-u is discussed. When the thickness was reduced, the AOM for Pt 5d was nearly constant, whereas a weak increase was observed for Co 3d. Both AOMs are small in contrast to the large K-u, and any proportionality between AOM and K-u was hardly recognized. This result indicates that a large AOM is not always a necessary and sufficient condition for the appearance of perpendicular magnetization.

DOI： 10.1063/1.3186018

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We have investigated the effect of hydrogenation on La 5d and 6p electronic states in metallic LaHx (x0.0, 2.0, 2.3, and 2.6) by X-ray absorption near edge structure at the La L-edges. As the hydrogen content x increases from 0 to 2.6, white-line intensity at the La L2,3-edges shows a remarkable increase in the range of x>2.0. This is interpreted as the increase in La 5d hole induced by interstitial H atoms on the octahedral sites. On the other hand, the shoulder structure at the La L1-edge disappears in the process of x0.0rightarrow;2.0, indicating that the p-d hybridization is weakened by H atoms on the tetrahedral sites. This study demonstrates that H atoms on the two interstitial H sites provide different contribution to the modification of the electronic states. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/190/1/012070

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

The UV irradiation effect in the practical luminescence material (Pr, Al)-doped SrTiO3 was investigated by x-ray absorption spectroscopy at the Ti K-edge. Two characteristic peaks observed in difference spectra between UV off-and on-spectra show different UV energy dependence; above the common onset UV energy of similar to 3.3 eV, which is nearly equal to the band-gap energy, a difference peak at the main absorption edge changes its intensity in accordance with the photoluminescence excitation spectrum, while another difference peak in the pre-edge region does not. Through the consideration of the energy scheme, the Ti 3d conduction-band bottom is responsible for the pre-edge features and is rather insensitive to UV energy, whereas the main edge together with other features in the higher-energy region is attributable to the upper-lying 4p states that are strongly influenced by UV light via valence holes. These results enable us to propose a mechanism of UV absorption followed by visible light emission.

DOI： 10.1088/1742-6596/190/1/012083

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) in a filled skutterudite SmOs4Sb12 were measured at Os L-edge under multiple extreme conditions, T = 2.2 K, H = 10 T, and P up to 3.5 GPa in order to obtain information of Os 5d electronic states. At ambient pressure, small dichroic signal of 0.1% was clearly observed and the orbital and spin magnetic moments of Os 5d are estimated to be -0.001 mu(B) and 0.012 mu(B), respectively. At high pressure, the XMCD intensity reaches a maximum around 0.6 GPa, and decreases with increasing pressure as to finally disappear at 3.5 GPa. This trend is similar to the reported magnetization under high pressure. The behavior of Os 5d electronic states strongly connects with a novel feature observed in SmOs4Sb12.

DOI： 10.1088/1742-6596/190/1/012020

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

In order to probe pressure-induced modification in Co magnetic state in Laves phase RCo2 (RDy, Ho, and Er) compounds, we have measured X-ray magnetic circular dichroism (XMCD) under high pressure. The R L2-edge XMCD indicates that Co magnetic moment MCo gradually decreases as the pressure increases. The Co K-edge XMCD shows that the effect of R molecular field is significantly suppressed under high pressure. As a result, it is revealed that the pressure variation of MCo is closely associated with R-Co interaction. The Co magnetic state is separately discussed from that of R partner. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/190/1/012021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The Ti K x-ray absorption spectra of fine particles of the practical luminescence material (Pr, Al)-doped SrTiO(3) were measured under UV irradiation. Significant changes were induced by the UV irradiation both in the pre-edge region and in the 1s4p main absorption edge. Surprisingly, similar changes were observed for a SrTiO(3) single crystal in a quantum paraelectric state, which also emits a faint greenish light under strong UV irradiation. High-resolution x-ray diffraction measurements reveal that the electron charge-density distributions in the two samples are identical, which indicates that the photoabsorption mechanism of Ti(4+) ions in the oxygen octahedra is the same.

DOI： 10.1103/PhysRevB.78.073103

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Language：Japanese   Publisher：The Crystallographic Society of Japan  

X-ray magnetic circular dichroism (XMCD) is a powerful tool for studying the electronic and magnetic states in ferromagnetic materials. Beamline 39XU at SPring-8 has currently developed the material science using XMCD under high pressures. Here, we briefly review the experimental techniques and the recent outcome of the pressure-dependent XMCD in ferromagnetic Fe, Co, and Ni metals and itinerant ferromagnetic Mn<SUB>3</SUB>GaC. The extension to the experiment under multiple extreme conditions, i.e. low temperature, high magnetic field, and high pressure, is also prospected.

DOI： 10.5940/jcrsj.49.279

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Other Link： https://jlc.jst.go.jp/DN/JALC/00303281076?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We observed the spatially resolved X-ray absorption fine structure of meteoritic inclusion by photoelectron emission microscopy in conjunction with hard-X-ray synchrotron radiation. The cracked domain in the inclusion is identified as Cr2FeO4 (chromite), and its electronic structure shows identical behavior with that of synthetic chromite. The photon energy is also scanned over the extended region to obtain the radial distribution function. It finally shows almost identical behavior as synthetic chromite. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.05.048

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Photoelectron emission microscope (PEEM) with magnetic linear dichroism (MLD) is applied for reading magnetic information of meteoritic iron. We observed the ferromagnetic domain image on the bcc-FeNi lamella in Gibeon iron meteorite through MLD effect. The easy-axis in the observed magnetic domain aligns [1 1 0] or [1 1 0], and such behavior is unfavorable in synthetic bec-FeNi system usually showing the easy-axis of (100). This easy-axis rotation can be reasonably explained by induced magnetic anisotropy. It suggests that bcc-FeNi lamella has grown along (I 10) direction with extremely slow developing process. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2007.04.196

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The stability of the ferromagnetic state in Fe, Co, and Ni metals under high pressure is studied using X-ray magnetic circular dichroism (XMCD) at the K-edge and X-ray powder diffraction. It is found that the ferromagnetic state under pressure is very different for Fe, Co, and Ni metals, and is closely associated with the crystal structure. In the case of Fe, the XMCD spectrum disappears with increasing pressure from 14.2 to 17.8 GPa, indicating the transition from a ferromagnetic to a nonmagnetic state. This transition results in the bcc --&gt; hcp martensitic transformation accompanied by a decrease in the c/a ratio of the hcp phase. In contrast to Fe, the dichroic amplitude in Co and Ni decreases slightly under the applied pressure. The ferromagnetic states in Co and Ni metals are maintained even at 39 and 48 GPa, respectively. The stability of ferromagnetism is interpreted from the viewpoint of electronic states.

DOI： 10.1143/JPSJ.76.064703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements have demonstrated the modification of the magnetic moment of Co in ErCo2 induced by applying pressure. Co K-edge and Er L-2-edge XAS and XMCD spectra recorded under applied hydrostatic pressures up to 4.2 GPa reveal that the modification of the magnetic properties of Co proceeds through two different pressure regimes. At low pressure, the Co atoms show an ordered magnetic moment induced by the effective field created by the Er sublattice. The Co moment progressively diminishes as the applied pressure increases, but it is not canceled for applied pressures of up to 4.2 GPa. The results show that the pressure mainly affects the Co subsystem without affecting the magnetism of the Er sublattice.

DOI： 10.1103/PhysRevB.75.180402

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We present an x-ray magnetic circular dichroism (XMCD) study performed at the Co K edge and at the Er L-2,L-3 edges in the Er1-xYxCo2 series. Our results indicate that both Er and Co magnetic sublattices order at the same temperature for all the investigated compounds. In the case of the Er0.6Y0.4Co2 compounds, XMCD data do not show the decoupling of the magnetic ordering for both Er and Co sublattices. Moreover, no experimental evidence of the occurrence of an inverse itinerant electron metamagnetism has been found for applied magnetic fields of up to mu H-0=10 T. In addition, a nonzero magnetic moment is found at the Co sites in the case of the Er0.5Y0.5Co2 compound.

DOI： 10.1103/PhysRevB.75.144405

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We present an x-ray magnetic circular dichroism (XMCD) study performed at both the Co K edge and the Lu L-2,L-3 edges on (YyLu1-y)(Co1-xAlx)(2) systems. The XMCD spectra reflect the different magnetic character of these systems, allowing us to monitor the transition from weak to strong ferromagnetism. The XMCD at the Lu L-2,L-3 edges indicates the existence of an ordered 5d moment at the lutetium sites that is coupled antiparallel to the Co moment. Estimates of the magnetic moment of Lu have been obtained by applying the XMCD sum rules. Our results show that there is a correlation between the Lu 5d-induced magnetic moment and the magnetic character of the (YyLu1-y)(Co1-xAlx)(2) compounds. These results suggest that the developing of the Lu moment plays an important role in reinforcing the magnetic interactions and favoring the ferromagnetic character of the Lu-rich compounds.

DOI： 10.1103/PhysRevB.75.064410

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Language：English   Publishing type：Research paper (international conference proceedings)  

We report on a transition metal contribution to the rare-earth L 2-edge XMCD spectrum of intermetallic rare-earth - transition metal compounds (R-T). The shape and location of this contribution is independent on both the specific rare-earth and the specific 3d metal in the compound. The evolution of the signal with the 3d content indicates that the signal is proportional to the number of T neighboring atoms around the absorbing R atom. In addition, comparison between Fe and Co Laves compounds indicates that the signal also resembles the magnetic moment of the T metal. Comparison with other R:T series shows that the presence of a T contribution is not a particularity of Laves phases but a general result. © 2007 American Institute of Physics.

DOI： 10.1063/1.2644566

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

X-ray diffraction patterns and L-III-edge x-ray absorption near edge structure (XANES) spectra of YbInAu2 and LuInAu2 compounds have been measured at high pressure and room temperature using a diamond anvil cell and a synchrotron radiation at SPring-8. YbInAu2 is more compressible at pressures lower than 4 GPa than above it; the evaluated bulk modulus by Birch-type equation of state is 54.7 GPa which is one-half of that of the LuInAu2 (112.5 GPa). The mean valence (v) over bar of Yb ion in YbInAu2 determined by the XANES measurement is an increasing function of pressure: 2.71(2) at normal pressure and 2.94(2) at 10 GPa. The rate of increase in (v) over bar with pressure is two times larger at pressures below 4 GPa than that above 4 GPa. However, the (v) over bar is described by a linear increasing function of the lattice compression: (v) over bar = (v) over bar (0)+2.9 parallel to Delta V/V-0 parallel to where (v) over bar (0) is 2.71. The extrapolation to the trivalent state gives the critical pressure of 13 GPa. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2335388

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Surface Science Society of Japan  

We demonstrate a new use for photoelectron emission microscopy (PEEM) in combination with hard X-ray synchrotron radiation. With this technique, an X-ray absorption fine structure spectrum can be acquired on each pixel in the observed image, thereby enabling analysis of the electronic properties in nanometer scale. Here, we report the local chemical composition and electronic structure of the Widmanstätten pattern in the Gibeon iron meteorite and clarify that the α lamella exhibits bcc structure with a spatially homogeneous Fe concentration. [DOI: 10.1380/ejssnt.2006.490]

DOI： 10.1380/ejssnt.2006.490

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.72.052412

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.72.052412/fulltext

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

The magnetic properties of a few atomic Pt layers on a 15-nm-thick Co film were studied by x-ray magnetic circular dichroism spectroscopy at the Pt L-2,L-3 edges. The spin and orbital magnetic moments of the Pt 5d electrons were separated using the sum rules, and the depth profiles of these moments were determined as a function of the distance from the Co-Pt interface. A Pt atom has a total magnetic moment of 0.61 mu(B)/atom at the interface, and the moment decreases exponentially with the distance from the interface with a characteristic decay length of 0.41 nm. Four atomic Pt layers near the interface possess 90% of the total magnetization of Pt. The Pt orbital magnetic moment is more than 15% relative to the spin moment and confined to two atomic layers near the interface. The orbital moment was found to be isotropic in the dichroism measurements using external magnetic fields perpendicular and parallel to the film plane. These properties of Pt magnetization are discussed in the context of thermal stability of magnetic recording media covered with a thin Pt overlayer.

DOI： 10.1103/PhysRevB.72.054430

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Pressure effects of the magnetic phase transition in DyCo2 were studied by XRD and XMCD. The magnetic transition changes from 1st order to 2nd order in a range of 4-5 GPa. The Co K-edge XMCD is insensitive to the pressure, which is interpreted as resulting mainly from the pressure variation of Dy 4f magnetic polarization. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2005.05.041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The magnetic properties of a few atomic Pt layers on a 15 nm thick Co film were studied by X-ray magnetic circular dichroism spectroscopy at the Pt L-2,L-3 edges. The spin and orbital magnetic moments of the Pt 5d electrons were separated using the magneto-optical sum rules. The Pt magnetization pro. le as a function of distance from the Co-Pt interface was determined using data from a series of films with various Pt thicknesses. This magnetization pro. le was approximated by an exponential function with a decay length of 0.41 nm, which characterizes the effective range of the magnetic coupling between Co and Pt. The total magnetic moment of a Pt atom at the interface was 0.7 mu(B)/atom including a 13% orbital moment. This is discussed in the context of the thermal stability of magnetic recording media capped with a thin layer of Pt.

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DOI： 10.1016/j.ssc.2005.03.025

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To study pressure-induced ferromagnetic state in Mn3GaC perovskite, we have performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ga K-edge under high pressure up to 29.4 GPa at room temperature. Ga K-edge XMCD was observed under pressure ranging from 4.5 to 29.4 GPa and results indicate that the Ga atom is magnetically polarized under high pressure. From the XMCD spectral profile, it is suggested that the pressure-induced ferromagnetic state has a canted ferromagnetic structure. © Physica Scripta 2005.

DOI： 10.1238/Physica.Topical.115a00591

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The magnetic properties of a few atomic Pt layers on a 15nm thick Co film were studied by x-ray magnetic circular dichroism spectroscopy at the Pt L 2,3 edges. The spin and orbital magnetic moments of the Pt 5d electrons were separated using the magneto-optical sum rules. The Pt magnetization profile as a function of distance from the Co-Pt interface was determined using data from a series of films with various Pt thicknesses. This magnetization profile was approximated by an exponential function with a decay length of 0.41nm, which characterizes the effective range of the magnetic coupling between Co and Pt. The total magnetic moment of a Pt atom at the interface was 0.7μB/atom including a 13% orbital moment. This is discussed in the context of the thermal stability of magnetic recording media capped with a thin layer of Pt. © Physica Scripta 2005.

DOI： 10.1238/Physica.Topical.115a00580

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

To study pressure-induced ferromagnetic state in Mn3GaC perovskite, we have performed X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy at the Ga K-edge under high pressure up to 29.4 GPa at room temperature. Ga K-edge XMCD was observed under pressure ranging from 4.5 to 29.4 GPa and results indicate that the Ga atom is magnetically polarized under high pressure. From the XMCD spectral pro. le, it is suggested that the pressure-induced ferromagnetic state has a canted ferromagnetic structure.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

An experimental system for X-ray magnetic diffraction (XMD) under extreme conditions was constructed on the beamline BL39XU at SPring-8. This system aims at studying magnetic properties of ferromagnets through the measurements of magnetic form factors under the conditions of low temperature (5 K), high magnetic field (6 T) and high pressure (70 GPa). This system consists of a superconducting magnet (SCM), a diamond anvil cell (DAC), a two-axis manipulator for the DAC, a five-axis goniometer for the SCM, and an X-ray polarizer with a phase plate. Details of this system are presented. Experimental results on uranium telluride are shown as a performance test with this instrumentation. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2004.08.025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Direct observation of aqueous fluids coexisting with MgSiO3 (enstatite) and/or Mg2SiO4 (forsterite) was performed at 0.5-5.8 GPa and 800-1000 degreesC with an externally heated diamond-anvil cell and synchrotron X-rays. At 1000 degreesC in the MgSiO3-H2O system, forsterite crystallizes below 3 GPa but not above that pressure. At 1000 degreesC in the Mg2SiO4-H2O system, forsterite congruently dissolves into the aqueous fluids up to 5 GPa. These observations suggest that the aqueous fluids coexisting with enstatite and forsterite have Mg/Si &lt; 1 below 3 GPa and 1 &lt; Mg/Si &lt; 2 above that pressure.
Comparison with the previous studies reporting Mg/Si ratios of the aqueous fluid coexisting with enstatite and forsterite indicates that the Mg/Si ratios change rapidly from SiO2-rich to MgO-rich at around 3 GPa and 1000 degreesC. This change can be related to possible structural changes of liquid water under these conditions. The aqueous fluids coexisting with enstatite and forsterite do have Mg/Si ratios similar to those found in the partial melts of H2O-saturated peridotite. Somewhere within the upper mantle, these two fluids unite to form a single regime and cannot be distinguished from each other.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In order to study the magnetic phase transition in Mn3ZnC at 233 K, X-ray magnetic circular dichroism (XMCD) has been measured at the Mn K-edge as a function of temperature and magnetic field. When the transition appears, the spectral intensity shows an abrupt increase with decreasing temperature and a linear reduction with increasing magnetic field. The present results provide evidence that orbital angular momentum is closely associated with the appearance of non-collinear magnetic structure due to the phase transition. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.06.045

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DOI： 10.1016/j.jallcom.2003.12.035

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.1143/jpsj.72.2372

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

X-ray magnetic circular dichroism (XMCD) of gamma'-iron nitride (Fe4N) was recorded at Fe K-edge under high pressue up to 27 GPa. The XMCD intensity decreased remarkably with pressure, and vanished at 24 GPa. Compressibility was measured by the X-ray diffraction method. These results indicate that Fe4N undergoes a second-order phase transition from the ferromagnetic state to a paramagnetic state without any structural change. The pressure-induced demagnetizing process is discussed in terms of the Fe magnetic states in the local environment.

DOI： 10.1143/JPSJ.72.2372

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Ce unoccupied 5d electronic states of the nonmagnetic heavy-fermion compound CeRu2Si2 have been investigated by means of x-ray magnetic circular dichroism (XMCD) experiments. We measure the magnetic field dependences of the Ce L-2,L-3-edge XMCD of a powder sample with a transmission mode at about 2 K. The magnetic field dependence of the L-2-edge x-ray absorption spectrum shows a slight enhancement of the white line with metamagnetic behaviour, indicating reduction of the c-f hybridization. The L-2 XMCD spectrum shows a single positive lobe, while the L-3 XMCD spectrum consists of a main negative peak and two small negative satellite peaks. The main structure of CeRu2Si2 is similar to that of CeRu2Ge2.

DOI： 10.1088/0953-8984/15/28/345

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DOI： 10.1016/s0038-1098(02)00889-x

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DOI： 10.1016/S0038-1098(03)00491-5

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DOI： 10.1016/S0038-1098(02)00889-X

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DOI： 10.1088/0953-8984/14/21/304

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DOI： 10.1088/0953-8984/14/44/441

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Low-temperature magnetic structures of an [Fe/Gd](15) multilayer are determined using the resonant X-ray magnetic scattering technique at a synchrotron source. The difference intensities of specular Bragg reflections observed by flipping the helicity of circularly polarized probing X-rays of energy close to the L-3 absorption edge of Gd show that the multilayer is in the Gd-aligned state with the magnetic moments of the Gd layers oriented parallel to the applied in-plane field at H = 0.5 kOe, T = 10 K. This transforms into the twisted state with canted Gd moments by raising field strength H and/or temperature T. In the twisted state, the Gd moments at the interfaces and the core of the Gd layers show distinctive canting angles. Temperature and field-dependent in-plane rotations of local Gd moments have been visualized.

DOI： 10.1143/JJAP.41.1331

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The effect of pressure on the structural stability of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals forming from a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass with a supercooled liquid region of 44 K has been investigated by in situ high-pressure angle-dispersive x-ray powder diffraction at ambient temperature using synchrotron radiation. The icosahedral quasicrystal structure is retained up to the highest hydrostatic pressure used (approximately 28 GPa) and is reversible after decompression. The bulk modulus at zero pressure and its pressure derivative of the icosahedral Zr-Al-Ni-Cu-Ag quasicrystal are 99.10+/-1.26 GPa and 4.25+/-0.16, respectively. The compression behavior of different Bragg peaks is isotropic and the full width at half maximum of each peak remains almost unchanged during compression, indicating no anisotropic elasticity and no defects in the icosahedral Zr-Al-Ni-Cu-Ag quasicrystals induced by pressure. (C) 2001 American Institute of Physics.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本物理学会  

DOI： 10.1143/JPSJ.70.1162

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DOI： 10.1103/PhysRevB.64.132101

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.64.132101/fulltext

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DOI： 10.1088/0953-8984/13/9/316

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Language：Japanese   Publisher：The Crystallographic Society of Japan  

The article reviews the recent determination of the magnetic structures of an [Fe/Gd] <SUB>15</SUB> multilayer by the authors using resonant magnetic scattering of circular polarized x-rays at synchrotron sources.The specular reflections reveal that the 5.4-nm-thick Gd layers magnetize highly nonuniformly along the out-of-plane direction in both magnitude and azimuthal angle in the aligned and twisted states of the sample. The decay of the <I>q<SUB>x</SUB></I>-scan magnetic diffuse scattering evidences much smoother magnetic interfaces than the charge interfaces.The <I>q<SUB>z</SUB></I>-dependent difference diffuse peaks suggest the presence of rough magnetic interfaces within the Gd layers.

DOI： 10.5940/jcrsj.41.298

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Other Link： https://jlc.jst.go.jp/DN/JALC/00064213644?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The magnetic structures of a (Fe/Gd)(15) multilayer are determined by resonant x-ray magnetic scattering using circular polarized light of energies tuned close to the Gd L and the Fe K absorption edges. Difference superlattice Bragg peaks observed by flipping the photon helicity show that the magnetic moments of the Gd layers are directed antiparallel to the in-plane applied held at temperatures higher than 180 K, and are twisted below. The local Gd magnetizations in each 5.4-nm-thick layer are highly nonuniform in both magnitude and twist angle in the out-of-plane direction: the interface sublayers nearly fully magnetize at room and low temperatures under the influence of the adjacent Fe magnetizations, whereas the central sublayers show measurable spontaneous magnetizations at 200 K and below. An application of the 1 -(T/T-c) law shows a reduced Curie temperature (T-c=214 K) compared with bulk Gd for the central sublayers, while T-c= 1023 K for the interface sublayers. The interface and central sublayers exhibit distinct twist behaviors as a function of temperature below the compensation temperature, indicating the short-range nature of the Fe-Gd interaction. The element-specific resonant x-ray scattering confirmed the antiferromagnetic arrangement of the Gd and Fe moments at room temperature.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC  

The q(z)-dependent sign of the X-ray charge-magnetic interference diffuse scattering observed from an Fe-Gd multilayer is found to be due to rough internal magnetic interfaces in the Gd layers. The internal magnetic roughness is correlated with the charge roughness of the Fe-Gd interface. Born-approximation calculations using a fractal interface model show that the internal and. Fe-Gd interfaces have similar magnetic roughness, as evidenced by the similar in-plane cut-off lengths of charge-magnetic height-height correlation functions.

DOI： 10.1098/rsta.1999.0468

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Charge-magnetic roughness correlations of the Gd layers in an Fe/Gd multilayer are studied using diffuse, x-ray resonant magnetic scattering. The strong interfacial coupling exhibited by this system, which restricts the orientation of the magnetic moments, makes possible a detailed study of the intrinsic charge-magnetic roughness. Quantitative analysis of the data is carried out by using a newly developed model, based on the Born approximation, for diffuse, x-ray resonant magnetic scattering from multilayers. Fits to the charge and charge-magnetic interference data result in longer correlation lengths for both in-plane and out-of-plane charge-magnetic roughness than for charge roughness. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevB.60.12234

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Resonant X-ray reflectivity intensities were collected at different X-ray energies near absorption edges in order to get element-specific density profiles for a (Gd/Fe)(10) multilayer. By fitting the measured resonant X-ray reflectivity curves simultaneously, atomic density profiles of Gd and Fe were determined. X-ray reflectivity intensities were also measured for elliptically polarized X-rays at Gd L-2, and L-3, edges with magnetic fields parallel and antiparallel to the helicity of the X-rays. Asymmetry ratios between the reflectivity intensities with opposite magnetic field directions were calculated from the obtained density profiles and compared with data. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0921-4526(98)00222-1

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DOI： 10.1016/S0921-4526(98)00219-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Bragg peaks are observed in difference resonant specular reflectivity signals from a GdCo/Ag multilayer in a flipping magnetic field for circularly polarized X-rays. The element-specific X-ray scattering at the L ₃ absorption edge of Gd directly evidences layers of magnetically ordered Gd ions stacked at a regular spacing of the multilayer 51 Å period. The Bragg peaks show a negative polarity, which is accounted for by the property of the resonant magnetic-charge interference scattering.

DOI： 10.1143/jjap.36.4525

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Other Link： https://iopscience.iop.org/article/10.1143/JJAP.36.4525/pdf

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DOI： 10.1107/S0909049597001441

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DOI： 10.11316/jpsgaiyo.67.1.4.0_817_2

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DOI： 10.11316/jpsgaiyo.64.2.3.0_375_3

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DOI： 10.11316/jpsgaiyo.63.2.4.0_894_4

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：INT UNION CRYSTALLOGRAPHY  

DOI： 10.1107/S0108767308081592

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DOI： 10.11316/jpsgaiyo.63.2.3.0_362_3

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DOI： 10.11316/jpsgaiyo.63.2.4.0_796_3

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