Rare-earth tuned magnetism and magnetocaloric effects in double perovskitesR₂NiMnO₆

We present a comprehensive experimental study of magnetization (2 <T< 300 K, 1 <H< 8 T) and magnetocaloric effect in double perovskite materialsR₂NiMnO₆withR= Pr, Nd, Sm, Gd, Tb, and Dy. While a paramagnetic to ferromagnetic transition, with T_Cin the range∼100-200K, is a common feature that can be attributed to the ordering of Mn⁴⁺and Ni²⁺magnetic moments, qualitatively distinct behavior depending on the choice ofRis observed at low temperatures. These low-temperature anomalies in magnetization are also manifest in the change in magnetic entropy, -ΔS, whose sign depends on the choice ofR. 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.