Structures, Magnetic And Transport Properties Of La_1/2(Pr_1/4+3y/4Ca_3/4-3y/4)_1/2Mn_1-yGa_yO₃

Structural, magnetic and transport properties of polycrystalline samples La_1/2(Pr_1/4+3y/4Ca_3/4-3y/4)_1/2Mn_1-yGa_yO₃ (Mn³⁺:Mn⁴⁺=5:3) are experimentally studied. The substitution of Ga³⁺ ion for Mn³⁺ ion suppresses the ferromagnetism and metallic conduction significantly. Curie temperature TC decreases linearly with the substitution at a rate of about 15.8 K per 1% Ga. Corresponding to the decrease of the curie temperature TC, the metal-insulator transition temperature TMI shifts to low temperature, while the resistivity sharply increases by three orders with increasing of Ga doping. For all samples, a maximal magnetoresistance is found near TMI, at the same time, a low-temperature magnetoressitance is observed far below TC, they evidently increase with increasing Ga concentration. In addition, analyses about macromagnetic properties imply the absence of the Pr³⁺ moment ordering at 2 K. Magnetic dilution and disorder effects caused by Ga doping as well as grain boundaries effects in polycrystalline samples should be responsible for the experimental results.