Effect of Elaborating Method on Magnetic and Magnetocaloric Properties of La_0.65Ca_0.35−xK_xMn0₃(0 ≤ x ≤ 0.2) Manganites

Abstract

A comparative study of the structural, magnetic, and magnetocaloric properties of La_0.65Ca_0.35−xK_xMn0₃ powder samples elaborated by solid-solid and sol-gel methods is given. The X-ray diffraction patterns at room temperature show that all our synthesized samples elaborated by both methods are single phase. Samples elaborated by solid-solid method crystallize in the orthorhombic structure (Pbnm space group) for x ≤ 0.1 and in the rhombohedral one (R-3C space group) for x= 0.2, while for x = 0.15, the system begins to exhibit both phases with different proportions. The structural transition from Pbnm space group to R-3C one occurs for x > 0.15 for samples elaborated by sol-gel method. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our studied samples display a paramagnetic ferromagnetic transition with decreasing temperature. Curie temperature T_C increases with increasing K content. It increases from 248 K for x = 0 to 310 K for x = 0.2 for samples elaborated by solid-solid method and from 275 K for x = 0 to 320 K for x = 0.2 for samples elaborated by sol-gel route. The maximum of the magnetic entropy change ${\mathrm {\Delta } S}_{M}^{\text {Max}}$ under Δμ₀H= 5 T is obtained for x = 0.2 sample elaborated by both methods. ${\mathrm {\Delta } \mathrm {S}}_{\mathrm {M}}^{\text {Max}}$ is found to be 5.78 J/kg/K at 305 K and 7.5 J/kg/K at 325 K for sample elaborated by solid-solid and sol gel, respectively. The relative cooling power RCP exhibits a maximum value of 313 J/kg at Δμ₀H= 5 T for x = 0.05 elaborated by solid-solid method and 300 J/kg at Δμ₀H= 5 T for x = 0.2 elaborated by sol-gel method.