Effects of partial Mn-substitution on magnetic and magnetocaloric properties in Pr_(0.7)Ca_(0.3)Mn_(0.95)X_(0.05)5O_3 (Cr, Ni, Co and Fe) manganites

摘要

Structural, magnetic and magnetocaloric properties of Pr_(0.7)Ca_(0.3)Mn_(0.95)X_(0.05)5O_3 (X = Cr, Ni, Co and Fe) ceramics have been investigated by X-ray diffraction (XRD) and magnetic measurements. Powder samples have been elaborated using the solid state reaction method at high temperature. The Rietveld analysis of the powder X-ray diffraction shows that the samples crystallize in the orthorhombic structure with Pnma space group. Magnetic measurements show that all our materials exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Arrott plots of ours materials reveal the occurrence of a second-order phase transition. The maximum values of magnetic entropy change ΔS_M~(max) are 2.92, 2.96, 3.1, and 2.38 J kg~(-1)K~(-1) and the relative cooling power (RCP) values are 405.8, 378.2,352.2 and 337.4J kg~(-1) for a magnetic-field change from 0 to 5 T for Cr, Ni, Co and Fe respectively. The large RCP found in our substituted samples will be interesting for magnetic refrigeration over a wide temperature range ~130 K around its paramagnetic to ferromagnetic transition temperature. With the scaling laws of ΔS_M, the experimental ΔS_M collapse onto a universal curve for several ceramics, where an average curve is obtained. With the phenomenological universal curve, the experimental ΔS_M are well predicted for all materials.