The Relation of the Magnetoresistance and Magnetic Frustration among Ferromagnetic Clusters in La(Mn_1-xNi_x)O_3+δ

摘要

Colossal magnetoresistance (CMR) properties of La(Mn_1-xNi_x)O_3+δ (0≤x≤0.1) are investigated. The partial replacement of Mn³⁺ by Ni²⁺ causes the conversion of Mn³⁺ to Mn⁴⁺. However, the CMR effect of the manganites with excess oxygen decreases as the Ni amount is increased. The samples were prepared both in air and in oxygen atmosphere in order to change the Mn⁴⁺ ratio and the concentration of Mn⁴⁺ was determined quantitatively. We measured the temperature dependence of magnetization after cooling the sample in zero field (ZFC) or in the field (FC). According to the temperature dependence of coercive field and thermoremanent magnetization, a cluster glass like transition is presumed. We propose that the frustration of the interaction among ferromagnetic clusters introduced by substituting Ni for Mn causes the decrease and increase of the magnetoresistance.