Effect of potassium doping on physical properties of perovskites La_(0.8)Cd_(0.2-x)K_xMnO_3

摘要

Polyoystalline perovskite manganites La_(0.8)Cd_(0.2-x)K_xMnO_3 (x = 0.05, 0.075 and 0.1) were prepared by sol-gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral (R3c) structure with increasing the K content. Magnetization as a function of temperature, M(T), shows that these compounds exhibit a paramagnetic (PM) to ferromagnetic (FM) phase transition with decreasing temperature. The Curie temperature (T_c) increases from 260 to 282 K as K-doping increases from 0.05 to 0.1. The resistivity measurements reveal that the samples exhibit a metallic to semiconductor transition and the electrical temperature transition T_P presents a similar trend of T_c, with increasing the K content. The magnetic entropy change |Δ S_M| has been deduced by two methods: a Maxwell relation, and the Landau theory. The maximum value of the magnetic entropy change obtained from the M(H) plot data is |ΔS_M~(max)| ~ 3.25Jkg~(-1) K~(-1) for applied magnetic field of 2 T. At this value of magnetic field the relative cooling power (RCP) is 62.59 J kg~(-1). Close to T_c, large change in magnetic entropy has been observed in all samples. Our result on magnetocaloric properties suggests that La_(0.8)Cd_(0.2-x)K_xMnO_3 compounds are attractive as a possible refrigerant for near room temperature magnetic refrigeration.