Spin fluctuations in oxygen doped layered perovskite cobalt oxide

酸素ドープしたペロブスカイトCo酸化物の磁気揺動

中島 健次  ; 梶本 亮一  ; 山田 和芳*; 堀金 和正*

Nakajima, Kenji; Kajimoto, Ryoichi; Yamada, Kazuyoshi*; Horigane, Kazumasa*

遷移金属酸化物へのキャリアドープは、非常に様々な現象を引き起こし集中的な研究の対象となってきた。層状酸化物LaMO(M: 3d金属)は、そのような研究モデル物質の1つであるが、Co系については、Coのスピン状態が種々の状態を取り得るなどさらに複雑性を持つ。そのような中で、我々は酸素ドープしたLaCoOの単結晶について、四季分光器を用いて磁気揺動の測定を行った。

Carrier doping into transition metal oxides triggers various phenomena, which have been subjected to intensive investigations. Layered oxide LaMO (M: 3d metal) is one of the model systems for such studies. In cobalates, contribution of orbital moment and possible spin state of Co give further complexity. In LaSrCoO, charges order in checker-board style and Co spin correlations are modulated in momentum space by the ordered charges. (1) Magnetic excitations in this system are reported to be accounted for spin-waves of Co spins taking into account the orbital moment. (2) In this study, we have investigated magnetic excitations in another almost half-doped system LaCoO by inelastic neutron scattering. Clear spin-wave excitations consistent to previous report on LaSrCoO were observed. However, we also observed an additional excitations with different zone center positions as well as excitation with higher spin-wave velocity. We expect detail analysis of present results can provide a key clue to understand the mechanism of complicated magnetic excitations caused by doped carrier, spin-orbital coupling and spins in transition metal oxides.