[12p-M101-1~14] 10.4 半導体スピントロニクス・超伝導・強相関

▲ [12p-M101-5] Inter-valence Charge Transfer in a Ru-doped Cobalt Ferrite CoFe₂O₄ Thin Film

〇MASAKI KOBAYASHI^1,2、MUNETOSHI SEKI^1,2、MASAHIRO SUZUKI³、MIHO KITAMURA⁴、ATSUSHI FUJIMORI³、KOJI HORIBA⁴、HIROSHI KUMIGASHIRA⁴、MASAAKI TANAKA^1,2、HITOSHI TABATA^1,2 (1.Univ. of Tokyo、2.CSRN, Univ. of Tokyo、3.Dep. Phys., Univ. of Tokyo、4.KEK-IMSS)

キーワード：Ferromagnetic semiconductor, Spinel ferrite, X-ray absorption spectroscopy

To fabricate spintronic devices such as magneto-resistive random-access memory and spin transistors, ferromagnetic semiconductors with the Curie temperatures (T_C > 300 K) are needed. Spinel ferrite M²⁺Fe₂O₄ (M = Mg, Mn, Co, etc) shows semiconducting conductivity at room temperature because the valence state of Fe ion is 3+ and there is no carrier hopping on the B sites. Substituting an ion having the valence higher than 3+ for the cation site M leads to a mixed valence state of Fe²⁺/Fe³⁺ on the B site in M²⁺Fe₂O₄, resulting in the increase of the electric conductivity as in the case of Fe₃O₄. Actually, Ru doping on cobalt ferrite CoFe₂O₄ (CFO) thin films dramatically improves the conductivity. It is expected that this improvement of the conductivity originates from inter-valence charge transfer between the Fe 3d and Ru 4d orbitals; Fe³⁺ + Ru³⁺ à Fe²⁺ + Ru⁴⁺. In this study, we have conducted x-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (RPES) on CFO and Co_0.5Ru_0.5Fe₂O₄ (CRFO) thin films to investigate the change of the electronic states due to the Ru-doping on CFO.