Magnetocaloric effects and critical behavior of La0.65Ca0.35−xGdxMnO3 (0≤x≤0.15)

Abstract

In this study, we investigate the magnetocaloric effects (MCE) and critical behavior of Gd-doped La[Formula: see text]Ca[Formula: see text]GdxMnO3 ([Formula: see text]) polycrystalline materials. Our results reveal excellent MCE in the Gd-doped samples. Under a magnetic field of 7[Formula: see text]T, the full-width at half maximum ([Formula: see text] increases from 41[Formula: see text]K ([Formula: see text]) to 121[Formula: see text]K ([Formula: see text]) and 112[Formula: see text]K ([Formula: see text]). Additionally, the refrigerant capacity (RC) is enhanced by 149% and 145% at [Formula: see text] and [Formula: see text], respectively, compared to the parent phase. We propose that these improvements can be attributed to the introduction of Gd[Formula: see text] ions, which possess smaller ionic radii. This reduction in the average A-site ionic radius weakens the double exchange (DE) interactions, resulting in a more continuous phase transition within the system. Supporting this view, we observe a decrease in magnetization strength after doping, a reduction in Curie temperature ([Formula: see text] from 250[Formula: see text]K ([Formula: see text]) to 134[Formula: see text]K ([Formula: see text]) and 130[Formula: see text]K ([Formula: see text]) and a transformation from a first-order to a second-order phase transition in the doped samples. To characterize the critical behavior of the phase transition in the doped samples, we employ the K-F method. The obtained critical exponents for [Formula: see text] and [Formula: see text] are [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], [Formula: see text], respectively. Furthermore, the calculation of the n values suggests a transition of the phase transition in the doped samples from short-range ordering to long-range ordering.