S.-I. Fujimori

Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism

We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p -> 3d XMCD ...

Electronic configuration of Mn ions in the π-d molecular ferromagnet β-Mn phthalocyanine studied by soft X-ray magnetic circular dichroism

Abstract We have studied the electronic structure of the molecular ferromagnet β -Mn phthalocyanine ( β -MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T 8.6 K , by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental results and subsequent cluster-model calculation, we find that the ferromagnetic Mn ion in β -MnPc is largely in the 4 E g ground state arising from the ( e g ) 3 ( b 2 g ) 1 ( a 1 g ) 1 [ ( d x z , y z ) 3 ( d x y ) 1 ( d z 2 ) 1 ] configuration of the Mn2+ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the 4 E g ground state originates from the a 1 g orbital of the Mn2+ ion, it is proposed that a 1 g – a 1 g exchange coupling via the π orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of β -MnPc.

Soft x-ray magnetic circular dichroism study of weakly ferromagnetic Zn1−xVxO thin film

The authors performed a soft x-ray magnetic circular dichroism (XMCD) study of a Zn1−xVxO thin film, which showed a small ferromagnetic moment. Field and temperature dependences of V 2p XMCD signals indicated the coexistence of Curie-Weiss paramagnetic and antiferromagnetic V ions, quantitatively consistent with the magnetization measurements. The authors attributed the paramagnetic signal to V ions substituting for Zn sites, which are somewhat elongated along the c axis. A possible formation of ferromagnetically dead layers in the surface region of the film is also discussed.

Photoemission and x-ray absorption studies of valence states in (Ni,Zn, Fe,Ti)3O4 thin films exhibiting photoinduced magnetization

By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼230K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼230K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.

Local electronic structure of Cr in the II–VI diluted ferromagnetic semiconductor Zn1-xCrxTe

The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn1-xCrxTe (x=0.03 and 0.15) thin films has been investigated using x-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). Magnetic-field (H) and temperature (T) dependences of the Cr 2p XMCD spectra correspond well to the magnetization measured by a SQUID magnetometer. The line shape of the Cr 2p XMCD spectra is independent of H, T and x, indicating that the ferromagnetism originated from the same electronic states of the Cr ion. A cluster-model analysis indicates that although there are two or more kinds of Cr ions in the Zn1-xCrxTe samples, the ferromagnetic XMCD signal originated from Cr ions substituted for the Zn site. The Cr 3d partial density of states extracted using Cr 2p→3d resonant PES shows a broad feature near the top of the valence band, suggesting strong s,p–d hybridization. No density of states is detected at the Fermi level, consistent with their insulating behavior. Based on these findings, we conclude that the double-exchange mechanism cannot explain the ferromagnetism in Zn1- xCrxTe.

Fermi Surface Variation of Ce 4f-electrons in Hybridization Controlled Heavy-Fermion Systems

Abstract Ce 3d–4f resonant angle-resolved photoemission measurements on CeCoGe 1.2 Si 0.8 and CeCoSi2 have been performed to understand the Fermi surface topology as a function of hybridization strength between Ce 4f- and conduction electrons in heavy-fermion systems. We directly observe that the hole-like Ce 4f-Fermi surfaces of CeCoSi2 is smaller than that of CeCoGe 1.2 Si 0.8 , indicating the evolution of the Ce 4f-Fermi surface with the increase of the hybridization strength. In comparison with LDA calculation, the Fermi surface variation cannot be understood even though the overall electronic structure is roughly explained, indicating the importance of strong correlation effects.

Electronic structure of URu2Si2 in paramagnetic phase studied by soft x-ray photoemission spectroscopy

We have performed soft x-ray photoemission spectroscopy study on the heavy-fermion compound URu2Si2. We have found that the U 5f states are distributed in the binding energy range between 0.6 eV and the Fermi level. In angle-resolved photoemission spectra, we have observed the U 5f-Ru 4d hybridized band. Our results strongly suggest that the U 5f states form itinerant energy bands in this system.

Electronic structure analysis of UIr using soft x-ray photoemission spectroscopy and band calculation

Uranium ferromagnet UIr is well-known to a pressure-induced superconductor without an inversion symmetry. In order to clarify the U 5f states of ferromagnetically-ordered UIr below Tc ~ 46 K and at ambient pressure, we observed 5f-sensitive soft X-ray photoemission spectra (SXPES), and calculated the band structure by a relativistic LAPW method in a local-spin density approximation. The temperature-dependent angle-integrated SXPES near the Fermi energy show a definite energy-shift of the band structures below and above Tc. The exchange splitting of the 5f bands seems to be consistent with an itinerant band picture like Stoner model. Furthermore the angle-resolved SXPES are compared with the theoretical band structure to investigate the relationship between the band shift and the magnetism.