Anomalous magnetic behavior for Mn-site doped La 0.7 Ca 0.3 MnO 3 : internal magnetic interactions and extrinsic inhomogeneity

Magnetic properties of Mn-site doped La0.7Ca0.3Mn0.94TM0.06O3+Δ (TM=Cu, Zn) were experimentally and theoretically studied. The low-temperature magnetization and magnetic phase transition temperature TC of the samples combining with simulations of 2D doped Ising model suggest that Cu2+ ions have an antiferromagnetic interaction with their nearest neighboring Mn ions. Interestingly, an anomalous magnetic behavior, a “step-like” magnetic phase transition, is observed. The existence and magnitude of this step vary with different doping ions and oxygen ratio, which is experimentally suggested to be relevant to the interaction between magnetic ions and oxygen content. A superposition between two independent magnetic systems with different values of an exchange integral J well explains the anomalous magnetic phase transition, which suggests that this step-like behavior results from extrinsic inhomogeneity and negligible coupling between grains in polycrystalline.