Study Of Structural, Magnetic And Electric Properties Of Perovskite Manganites Sm_0.5Ca_0.5Mn_1-xCr_xO₃

The double-doped perovskites-type manganite have a variety of physical phenomena, such as colossal magnetoresistance (CMR), charge-ordering (CO), electronic phase separation (EPS), etc. These rich and colorful phenomena are associated with strong correlation between spin, charge, orbital, and lattice degrees of freedom. With the changes of outside conditions (magnetic field, temperature and hole-doping), ferromagnetic (FM)-antiferromagnetic (AFM), insulator-metal etc. multiple competing phases will be induced. In this article, systematic studies of magnetic and electric transport properties have been performed on the Cr-doped Smo.5Cao.5Mni.,Crx03(x=0,0.025,0.05,0.10,0.20,0.30) system.In this dissertation, the series sample Sm0.5Ca0.5Mn1-xCrxO3(x=0,0.025,0.05,0.10,0.20,0.30) were prepared by traditional solid phase reaction. The microstructure and crystal cell parameters of a series of samples are determined by X-ray diffraction (XRD). The physics properties measurement system (PPMS) was used for measuring M-T, M-H, p-T, p-H curves of the series samples.X-ray diffraction pattern showed that all the samples are single-phase orthorhombic structure. At low temperatures, long range charge order (CO) is weakened by Cr doping even at doping concentration as low as2.5%. The ferromagnetic (FM) fraction increases with increasing Cr doping till x=0.10, and decreases by further Cr doping. The metamagnetic transition for x=0.05sample has been carefully studied and the origin is ascribed to the phase transition from CO antiferromagnetic (AFM) phase to FM phase in a phase separation scenario. Temperature dependence of resistivity curves evidenced charge-ordering and the CMR effect in the samples. X=0.05, and0.10samples displays metamagnetic transition appearance, with a transition temperature TIM=75K under zero field in the cooling process. Simultaneously, they demonstrate different hysteresis features. More generally, for x=0.05sample, if we keep increasing the field, TIM will increases and the resistivity will decrease. However, we suggest that the behavior of the metamagnetic transitions and CMR, and large residual resistance and relatively low value of magnetization in the FM state, are all consistent with the diffuse phase transition and phase separation.