From complex magnetic ground states to magnetocaloric effects: a review of rare earth R ₂ In intermetallic compounds

Abstract R 2 In (R = rare earth) intermetallics exhibit unusual magnetic and magnetocaloric properties, driven by subtle electronic effects, lattice distortions, and spin-lattice coupling. Most of these binary compounds adopt the hexagonal Ni 2 In-type structure at room temperature, with Eu 2 In and Yb 2 In stabilizing in the orthorhombic Co 2 Si-type lattice. While the lighter lanthanide compounds Eu 2 In and Pr 2 In undergo clear first-order magnetic phase transitions accompanied with negligible thermal hysteresis and minimal lattice volume change, the magnetic transition in Nd 2 In lies at the borderline between first- and second-order behavior. Notably, all three compounds exhibit a large magnetocaloric effect (MCE) in the cryogenic temperature range. In contrast, the heavy lanthanide R 2 In compounds, including Gd 2 In, display second-order magnetic transitions accompanied by a moderate MCE. No lanthanide-based R 2 In compound exhibits symmetry-breaking structural transition, while Y 2 In transforms from hexagonal to orthorhombic structure near 250 K. Secondary low-temperature transitions, including spin reorientation or antiferromagnetic ordering, further enrich the magnetic phase landscape in these compounds. Integrating theoretical descriptors such as charge-induced strain and electronic structure provides predictive insight into phase stability and magnetocaloric performance, guiding the design of rare-earth intermetallics with tunable magnetic properties for cryogenic applications.