Mean field magnetism and spin frustration in a double perovskite oxide with compositional complexity

With the rise of high entropy oxides, compositional disorder has emerged as a powerful tuning parameter for oxide-based functional properties, prompting the study of its influence on long-range magnetic ordering in double perovskite systems. In this work, we consider the RE2NiMnO6 (RE : rare-earth) family and investigate single-crystalline films of (La0.4Nd0.4Sm0.4Gd0.4Y0.4)NiMnO6. Despite configurational disorder and high cationic size variance at the RE-site, the material exhibits robust ferromagnetic ordering with a Curie temperature (Tc) of approximately 150 K, consistent with expectations based on the average ionic radii of the RE-sites in bulk RE2NiMnO6 family. Below Tc, Raman spectroscopy reveals deviations from anharmonic behavior, where the phonon renormalization aligns with a mean-field approximation of spin-spin correlation. At lower temperature, magnetic RE ions contribute to the magnetic behavior, and the system displays a reentrant spin-glass-like behavior. This study demonstrates that while a mean-field approach viably captures the long-range transition temperature, microscopic magnetic interactions are essential for understanding the low-temperature phase. Compositional disorder in high entropy oxides offers a novel approach to tuning functional properties, yet its impact on magnetic ordering in double perovskite systems remains underexplored. Here, the authors investigate high-entropy rare-earth double perovskite films, revealing robust ferromagnetic ordering and reentrant spin-glass behavior, highlighting the importance of microscopic interactions in low-temperature phases.