La-Co-Mn系酸化物の磁気抵抗と原子価状態

概要

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Magnetic and electric properties of LaCo_xMn_>1-x<O_3 (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) compounds were measured by applying the Superconducting Quantum Interference Device (SQUID) in the magnetic fields of 0 and 5 tesla at low temperatures. Respective atomic valences and the fraction of Co and Mn ions were also examined by an X-ray Photoelectron Spectroscopy (XPS) method at room temperature. Discrepancies in the electric resistivity (Magnetoresistance) of the compounds under the conditions with and without an applied magnetic field decreased with an increase of Co ion, and the maximum point of each magnetoresistance vs. temp. curve corresponded with the Curie temperature of transition from paramagnetic to ferromagnetic. Judging from the values of the effective magnetic moment obtained from Curie constant and as a result of deconvolution of the XPS spectrum, it was found that Co and Mn ions in the compounds coexisted respectively at the mixed valence states. The electron configuration of the former ion was low spin states of Co^II+ (t_>2g<^6 e_g^1) and Co^III+ (t_>2g<^6 e_g^0), whereas, that of the latter ion was high spin states of Mn^>3+< t(t_>2g<^3 e_g^1) and Mn^>4+< (t_>2g<^3 e_g^0). It is probable that, in the present system compounds, the ferromagnetic double exchange interaction between Mn^>3+< and Mn^>4+< ions dominates over that between Co^>II+< and Co^>III+< ions.
社団法人日本セラミックス協会の論文
2002-03-01