Rare-earth tuned magnetism and magnetocaloric effects in double perovskites $R_2$NiMnO${}_6$

Abstract

We present a comprehensive experimental study of magnetization and magnetocaloric effect (MCE) in double perovskite (DP) materials $R_2$NiMnO${}_6$ with $R=$ Pr, Nd, Sm, Gd, Tb, and Dy. While a paramagnetic to ferromagnetic transition, with T${}_{\mathrm{C}}$ in the range $\sim 100-200$K, is a common feature that can be attributed to the ordering of Mn${}^{4+}$ and Ni${}^{2+}$ magnetic moments, qualitatively distinct behavior depending on the choice of $R$ is observed at low temperatures. These low-temperature anomalies in magnetization are also manifest in the change in magnetic entropy, $-\Delta S_M$, whose sign depends on the choice of $R$. In order to understand these results, we present theoretical analysis based on mean-field approximation and Monte Carlo simulations on a minimal spin model. The model correctly captures the key features of the experimental observations.

arXiv comment9 pages, 7 figures, 2 Tables

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