Yuichi Fujita
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Research Interests
Yuichi Fujita has a total of 37 co-authors. Here are the top co-authors by number of shared publications:
- Yuya Sakuraba
Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, Tsukuba, Japan
9 shared publications - Yoshio Miura
Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
5 shared publications - Kohei Hamaya
Osaka University
3 shared publications - Shigenori Ueda
Research Center for Electronic and Optical Materials, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
3 shared publications - Akio Kimura
Hiroshima University
2 shared publications - Aurelie Spiesser
National Institute of Advanced Industrial Science and Technology (Japan)
2 shared publications
Latest Publications
- 8 September 2026
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 140 (10)
Spin magnetic moments in the half-metallic ferromagnet—ferromagnet interface region detected by depth-resolved x-ray magnetic circular dichroism
We study spin magnetic moments near half-metallic Co2FexMn1−xSi (CFMS)/metal interfaces using depth-resolved x-ray magnetic circular dichroism (XMCD) and analyze their robustness against thermal fluctuations. We prepare epitaxial magnetic multilayered films with CFMS/CoFe and CFMS/Ag interfaces and observe the x-ray absorption spectroscopy (XAS) and XMCD spectra for both the interfacial and inner CFMS regions. By analyzing the observed XAS and XMCD spectra, we approximately extract the Mn-related magnetic moments. The results show that the Mn spin magnetic moment at the CFMS/CoFe interface exhibits almost no reduction compared with that in the inner CFMS layer, in contrast to the significant reduction observed at the CFMS/Ag interface. This suggests that the CFMS/CoFe interface provides a larger interfacial exchange stiffness than the CFMS/Ag interface, consistent with theoretical interface exchange stiffness values obtained from first-principles calculations. Furthermore, the large exchange stiffness at the CFMS/CoFe interface leads to the high stability of local spin magnetic moments to thermal fluctuation, resulting in a weaker temperature dependence of the magnetoresistance (MR) ratio in current-perpendicular-to-plane giant MR devices with a CoFe/CFMS/Ag/CFMS/CoFe structure than in those with a CFMS/Ag/CFMS structure.
- 8 September 2026
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 140 (10)
Spin magnetic moments in the half-metallic ferromagnet—ferromagnet interface region detected by depth-resolved x-ray magnetic circular dichroism
We study spin magnetic moments near half-metallic Co2FexMn1−xSi (CFMS)/metal interfaces using depth-resolved x-ray magnetic circular dichroism (XMCD) and analyze their robustness against thermal fluctuations. We prepare epitaxial magnetic multilayered films with CFMS/CoFe and CFMS/Ag interfaces and observe the x-ray absorption spectroscopy (XAS) and XMCD spectra for both the interfacial and inner CFMS regions. By analyzing the observed XAS and XMCD spectra, we approximately extract the Mn-related magnetic moments. The results show that the Mn spin magnetic moment at the CFMS/CoFe interface exhibits almost no reduction compared with that in the inner CFMS layer, in contrast to the significant reduction observed at the CFMS/Ag interface. This suggests that the CFMS/CoFe interface provides a larger interfacial exchange stiffness than the CFMS/Ag interface, consistent with theoretical interface exchange stiffness values obtained from first-principles calculations. Furthermore, the large exchange stiffness at the CFMS/CoFe interface leads to the high stability of local spin magnetic moments to thermal fluctuation, resulting in a weaker temperature dependence of the magnetoresistance (MR) ratio in current-perpendicular-to-plane giant MR devices with a CoFe/CFMS/Ag/CFMS/CoFe structure than in those with a CFMS/Ag/CFMS structure.
- Open Access
- 28 October 2025
- Published by Taylor & Francis in Science and Technology of Advanced Materials
- Vol. 26 (1)
Comparative experimental and theoretical study on anomalous Nernst effect of Heusler alloy Co 2 FeSi thin film: estimation of on-site Coulomb interaction at Co site
Co2FeSi is considered a half-metallic ferromagnet and a Weyl semimetal, however, its predicted properties have been shown to be heavily influenced by how the on-site Coulomb interaction is incorporated, which remains controversial. In this study, we measure the anomalous Nernst conductivity (αxy) and anisotropic magnetoresistance (AMR) effect of a Co2FeSi thin film from low temperature to room temperature, and compare the results with those of first-principles calculations using different values for on-site Coulomb interaction at the Co site (UCo). Our measurements reveal that αxy is less than 0.1 A m−1 K−1 at room temperature and decreases slightly with the temperature. The observed values of αxy are more than one order of magnitude smaller than the predictions unless a small but finite UCo is incorporated. The AMR effect exhibits a notable sign change from negative to positive with increasing temperature, which is inconsistent with the predicted band structure calculated using a large UCo value. By combining these experimental observations with first-principles calculations, we estimate that the appropriate UCo value is approximately 1–2 eV. Our findings provide valuable insight into the correlation effect in Co2FeSi, emphasizing the critical role of the on-site Coulomb interaction in accurately describing the transport properties of Co-based Heusler alloys.
- 28 October 2025
- Published by Taylor & Francis in Science and Technology of Advanced Materials
- Vol. 26 (1)
Open AccessComparative experimental and theoretical study on anomalous Nernst effect of Heusler alloy Co 2 FeSi thin film: estimation of on-site Coulomb interaction at Co site
Co2FeSi is considered a half-metallic ferromagnet and a Weyl semimetal, however, its predicted properties have been shown to be heavily influenced by how the on-site Coulomb interaction is incorporated, which remains controversial. In this study, we measure the anomalous Nernst conductivity (αxy) and anisotropic magnetoresistance (AMR) effect of a Co2FeSi thin film from low temperature to room temperature, and compare the results with those of first-principles calculations using different values for on-site Coulomb interaction at the Co site (UCo). Our measurements reveal that αxy is less than 0.1 A m−1 K−1 at room temperature and decreases slightly with the temperature. The observed values of αxy are more than one order of magnitude smaller than the predictions unless a small but finite UCo is incorporated. The AMR effect exhibits a notable sign change from negative to positive with increasing temperature, which is inconsistent with the predicted band structure calculated using a large UCo value. By combining these experimental observations with first-principles calculations, we estimate that the appropriate UCo value is approximately 1–2 eV. Our findings provide valuable insight into the correlation effect in Co2FeSi, emphasizing the critical role of the on-site Coulomb interaction in accurately describing the transport properties of Co-based Heusler alloys.
- Open Access
- 7 February 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 109 (8) , 085109
Near-interface electronic and magnetic states of heterostructures probed by hard x-ray photoemission combined with x-ray total reflectionDepth-dependent electronic and magnetic states of and MgO capped thin films were measured by using hard x-ray photoemission spectroscopy (HAXPES) combined with x-ray total reflection (TR). TR-HAXPES revealed that the near-interface electronic and magnetic states of films differed from those of bulk measured in non-TR condition. The decrease of the Co and Mn magnetizations near the interface along the easy magnetization axis in the bulk region relative to those in the bulk region and the changes in the valence band profiles were experimentally detected by nondestructive HAXPES utilizing TR. The possible origin of the reduction of the Co and Mn magnetizations and the changes in the valence band profile near the interface was due to an enhanced spin-wave excitation originating from the weakened exchange interaction between the local magnetic moments compared to the bulk region of , which can slightly modify the valence band electronic states, near the interface at a finite temperature. These results suggest that the combination of HAXPES with TR is useful to experimentally detect the electronic and magnetic states of near-interface and buried bulk regions in nondestructive way for insulator/ferromagnet heterojunctions.- 7 February 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 109 (8) , 085109
Open AccessNear-interface electronic and magnetic states of heterostructures probed by hard x-ray photoemission combined with x-ray total reflectionDepth-dependent electronic and magnetic states of and MgO capped thin films were measured by using hard x-ray photoemission spectroscopy (HAXPES) combined with x-ray total reflection (TR). TR-HAXPES revealed that the near-interface electronic and magnetic states of films differed from those of bulk measured in non-TR condition. The decrease of the Co and Mn magnetizations near the interface along the easy magnetization axis in the bulk region relative to those in the bulk region and the changes in the valence band profiles were experimentally detected by nondestructive HAXPES utilizing TR. The possible origin of the reduction of the Co and Mn magnetizations and the changes in the valence band profile near the interface was due to an enhanced spin-wave excitation originating from the weakened exchange interaction between the local magnetic moments compared to the bulk region of , which can slightly modify the valence band electronic states, near the interface at a finite temperature. These results suggest that the combination of HAXPES with TR is useful to experimentally detect the electronic and magnetic states of near-interface and buried bulk regions in nondestructive way for insulator/ferromagnet heterojunctions. - 1 December 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 108 (24) , L241101
Role of on-site Coulomb interactions in the half-metallic Weyl ferromagnet candidate thin-filmWe investigated the element-specific electronic structure of a half-metallic Weyl ferromagnet candidate film by utilizing soft-x-ray resonant photoelectron spectroscopy and first-principles calculations with and without considering an on-site Coulomb interaction. An Fe resonant photoelectron experiment revealed that the Fe states exist around 2 and 4 eV below the Fermi energy. Our calculations, based on the generalized gradient approximation without considering a Coulomb interaction at the Fe site, successfully reproduced the experimentally observed Fe partial density of states. Our findings shed light on the highly controversial correlation effect of , offering valuable insights into its half metallicity and Weyl semimetallicity.- 1 December 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 108 (24) , L241101
Role of on-site Coulomb interactions in the half-metallic Weyl ferromagnet candidate thin-filmWe investigated the element-specific electronic structure of a half-metallic Weyl ferromagnet candidate film by utilizing soft-x-ray resonant photoelectron spectroscopy and first-principles calculations with and without considering an on-site Coulomb interaction. An Fe resonant photoelectron experiment revealed that the Fe states exist around 2 and 4 eV below the Fermi energy. Our calculations, based on the generalized gradient approximation without considering a Coulomb interaction at the Fe site, successfully reproduced the experimentally observed Fe partial density of states. Our findings shed light on the highly controversial correlation effect of , offering valuable insights into its half metallicity and Weyl semimetallicity.- Open Access
- 1 August 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 106 (7) , 075101
Direct probing of temperature-independent bulk half-metallicity in by spin-resolved hard x-ray photoemissionWe have performed the bulk-sensitive spin-resolved hard x-ray photoelectron spectroscopy (HAXPES) to directly clarify the spin-dependent valence band electronic states and spin polarization of -ordered as a predicted half-metal. The spin-resolved valence band HAXPES spectra clearly exhibited the difference in the majority and minority spin states in the bulk region of a 30-nm-thick thin film buried under a MgO(2 nm) layer at both temperatures of 21 and 300 K. As expected from the half-metallicity in , we found that the majority (minority) spin spectrum shows a metallic Fermi edge (a band gap), leading the high spin polarization of ∼90% at around the Fermi level at a temperature of 21 K. The spin-resolved HAXPES experiments revealed that the half-metallicity of in the bulk region is independent on the temperature up to 300 K. The experiments also revealed the slight changes in the majority spin spectral shapes and the shift of the valence band maximum of the minority spin states with temperature. By comparing the experimental results with the first-principles calculations at a finite temperature obtained by the disordered local moment method, it is suggested that the slight changes in the majority and minority spin HAXPES spectra of with temperature is mainly caused by the temperature-dependent Co electronic states. It is also suggested that the conduction band minimum of the minority spin states is located sufficiently above the Fermi level at temperature up to 300 K.- 1 August 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 106 (7) , 075101
Open AccessDirect probing of temperature-independent bulk half-metallicity in by spin-resolved hard x-ray photoemissionWe have performed the bulk-sensitive spin-resolved hard x-ray photoelectron spectroscopy (HAXPES) to directly clarify the spin-dependent valence band electronic states and spin polarization of -ordered as a predicted half-metal. The spin-resolved valence band HAXPES spectra clearly exhibited the difference in the majority and minority spin states in the bulk region of a 30-nm-thick thin film buried under a MgO(2 nm) layer at both temperatures of 21 and 300 K. As expected from the half-metallicity in , we found that the majority (minority) spin spectrum shows a metallic Fermi edge (a band gap), leading the high spin polarization of ∼90% at around the Fermi level at a temperature of 21 K. The spin-resolved HAXPES experiments revealed that the half-metallicity of in the bulk region is independent on the temperature up to 300 K. The experiments also revealed the slight changes in the majority spin spectral shapes and the shift of the valence band maximum of the minority spin states with temperature. By comparing the experimental results with the first-principles calculations at a finite temperature obtained by the disordered local moment method, it is suggested that the slight changes in the majority and minority spin HAXPES spectra of with temperature is mainly caused by the temperature-dependent Co electronic states. It is also suggested that the conduction band minimum of the minority spin states is located sufficiently above the Fermi level at temperature up to 300 K. - Open Access
Spin-scattering asymmetry at half-metallic ferromagnet/ferromagnet interface
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient ($\gamma$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with considering the presence of $\gamma$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for a large $\gamma$ at a half-metallic FM/FM interface and its impact on CPP-GMR effect even at RT.Open AccessSpin-scattering asymmetry at half-metallic ferromagnet/ferromagnet interface
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient ($\gamma$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with considering the presence of $\gamma$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for a large $\gamma$ at a half-metallic FM/FM interface and its impact on CPP-GMR effect even at RT. - 8 October 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (14) , L140403
Spin-scattering asymmetry at half-metallic-ferromagnet|ferromagnet interface
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient (). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with considering the presence of at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for a large at a half-metallic FM/FM interface and its impact on the CPP-GMR effect even at RT.- 8 October 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (14) , L140403
Spin-scattering asymmetry at half-metallic-ferromagnet|ferromagnet interface
We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient (). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with considering the presence of at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for a large at a half-metallic FM/FM interface and its impact on the CPP-GMR effect even at RT.- 9 November 2020
- Published by American Physical Society (APS) in Physical Review Materials
- Vol. 4 (11) , 114406
Effects of the atomic order on the half-metallic electronic structure in the Heusler alloy thin filmThe atomic order and its effect on the electronic structure is a key issue in the application of half-metallic Heusler alloys as spin-polarized electron sources. In this study, we investigated the atomic ordering and electronic structures of (CFGG) Heusler alloy thin films at various annealing temperatures using anomalous x-ray diffraction (AXRD) and hard x-ray photoelectron spectroscopy (HAXPES). AXRD measurements clearly showed that the Co-Fe disorder is large in the as-deposited state, which is reduced to almost zero by annealing at for 30 min. The reduction of the Co-Fe disorder explains the observed increase in the spin polarization of currents estimated by ordinary and anisotropic magnetoresistance measurements. The photoelectron spectra of the valence band in CFGG thin films with different agree well with the first-principles calculations that considers the atomic disorder. We also found that the characteristic peaks appearing in the valence band HAXPES spectra shifted to higher binding energies, compared to the calculated density of states for stoichiometric -ordered CFGG. This indicates that the Fermi level is shifted and located in the vicinity of the conduction band edge in the present CFGG thin film due to electron doping by a mildly Co-rich chemical composition. Our first-principles calculations of partial density of state of electron predicted that the high spin-polarization is obtainable in a wider energy region near Fermi level in the -ordered structure than the B2 structure, which explains the enhancement of spin-polarization by promoting -ordering in the present CFGG film.- 9 November 2020
- Published by American Physical Society (APS) in Physical Review Materials
- Vol. 4 (11) , 114406
Effects of the atomic order on the half-metallic electronic structure in the Heusler alloy thin filmThe atomic order and its effect on the electronic structure is a key issue in the application of half-metallic Heusler alloys as spin-polarized electron sources. In this study, we investigated the atomic ordering and electronic structures of (CFGG) Heusler alloy thin films at various annealing temperatures using anomalous x-ray diffraction (AXRD) and hard x-ray photoelectron spectroscopy (HAXPES). AXRD measurements clearly showed that the Co-Fe disorder is large in the as-deposited state, which is reduced to almost zero by annealing at for 30 min. The reduction of the Co-Fe disorder explains the observed increase in the spin polarization of currents estimated by ordinary and anisotropic magnetoresistance measurements. The photoelectron spectra of the valence band in CFGG thin films with different agree well with the first-principles calculations that considers the atomic disorder. We also found that the characteristic peaks appearing in the valence band HAXPES spectra shifted to higher binding energies, compared to the calculated density of states for stoichiometric -ordered CFGG. This indicates that the Fermi level is shifted and located in the vicinity of the conduction band edge in the present CFGG thin film due to electron doping by a mildly Co-rich chemical composition. Our first-principles calculations of partial density of state of electron predicted that the high spin-polarization is obtainable in a wider energy region near Fermi level in the -ordered structure than the B2 structure, which explains the enhancement of spin-polarization by promoting -ordering in the present CFGG film.- 20 August 2020
- Published by SPIE-Intl Soc Optical Eng
- Vol. 11470, 114700Z-32
Proximity exchange coupling across an MgO tunnel barrier detected via spin precession
Proximity exchange coupling across an MgO tunnel barrier is observed up to room temperature. The proximity exchange field, which ferromagnetic Fe exerts on the spin accumulation in a Fe/MgO/Si tunnel contact, modifies the spin precession of the spin accumulation at the MgO/Si interface and is detected via the inverted Hanle effect in a three-terminal configuration. It produces shifts and hysteresis of the inverted Hanle curves, and discontinuities at the coercive field of the ferromagnet, at which the magnetization and thereby the exchange field is reversed. The proximity exchange field is observed not only at low temperature, as we previously reported, but also at room temperature. We compare the magnitude of the exchange field at different temperatures, and complement this with data on the tunnel resistance and the tunnel spin polarization, which was extracted from four-terminal non-local spin transport in the same devices.
- 20 August 2020
- Published by SPIE-Intl Soc Optical Eng
- Vol. 11470, 114700Z-32
Proximity exchange coupling across an MgO tunnel barrier detected via spin precession
Proximity exchange coupling across an MgO tunnel barrier is observed up to room temperature. The proximity exchange field, which ferromagnetic Fe exerts on the spin accumulation in a Fe/MgO/Si tunnel contact, modifies the spin precession of the spin accumulation at the MgO/Si interface and is detected via the inverted Hanle effect in a three-terminal configuration. It produces shifts and hysteresis of the inverted Hanle curves, and discontinuities at the coercive field of the ferromagnet, at which the magnetization and thereby the exchange field is reversed. The proximity exchange field is observed not only at low temperature, as we previously reported, but also at room temperature. We compare the magnitude of the exchange field at different temperatures, and complement this with data on the tunnel resistance and the tunnel spin polarization, which was extracted from four-terminal non-local spin transport in the same devices.