Abstract
Magnetization relaxation, ac susceptibility, dc magnetization and magnetoelectrical transport measurements have been carried out on Al3+-doped manganites La0.5Ca0.5Mn1-xAlxO3-δ (x = 0.05, 0.07, 0.09, 0.10, 0.15). Experimental results suggest that nonmagnetic Al3+ substituting Mn suppresses the ferromagnetic phase and induces a charge ordered antiferromagnetic phase. The coexistence and competition of these two kinds of interactions result in a spin-glass like state in x = 0.1 and 0.15 system. Obvious hysteresis was observed in both magnetization and resistivity versus temperature and magnetic field curves, suggesting an inhomogeneous metastable phase transition. Upon applying a magnetic field of HCA-F, the Al3+-doped samples undergo an irreversible metamagnetic transition from the charge ordering antiferromagnetic insulating to ferromagnetic metallic phase in the low temperature region. Phase diagram in the HC-T plane has been determined according to the magnetization and magnetoelectric transport measurements. The magnetic disorders and antiferromagnetic matrix produced by Al3+ dopants and spontaneous oxygen vacancies play an important role in the pinning of the FM phase.
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