Instability of magnetization and resistivity in La0.5Ca0.5Mn1-xAlxO3 (0 ≤ x ≤ 0.025) ceramic manganites

Abstract

A detailed investigation of the thermal hysteresis, electrical and magnetic properties of La0.5Ca0.5Mn1-xAlxO3 manganites was carried out by resistivity and magnetization measurements. Rietveld refinement of X-ray diffraction patterns indicates an orthorhombic structure with Pnma space group for all samples. The magnetic susceptibility measurements on samples with Al doping up to x = 0.0125 indicated that the charge and orbitally ordered CE-type antiferromagnetic (AFM) state is suppressed and the ferromagnetic (FM) phase increases. With further increase in Al content the FM phase is also suppressed and an A-type AFM insulating state is stabilized. The thermal hysteresis decreases in the samples up to x = 0.0125 whereas it increases by further enhancement of doping up to x = 0.025. The rotation direction of the thermal hysteresis loop changes from counterclockwise to clockwise with increasing of Al doping. Also, the magnetization measurement indicates that saturation magnetization is initially enhanced by increasing doping level up to 0.0125 whilst it is slightly reduced by further increasing doping content. Magnetization versus magnetic field loops of samples at zero field cooled (ZFC) and field cooled (FC) modes at 5 K showed an instable behaviour in the low doping, while in high doping the magnetization curve of ZFC and FC overlapped, demonstrating the stable FM and AFM phases. The results of the resistivity measurements confirmed change in thermal hysteresis and thermal cycling. The thermal hysteresis and cycling behaviour are attributed to the interfacial elastic energy in the boundary between FM and CO–AFM phases.