From Complex Magnetic Ground States to Magnetocaloric Effects: A Review of Rare Earth R$_2$In Intermetallic Compounds

TL;DR

This review discusses the magnetic and magnetocaloric properties of R2In intermetallic compounds, highlighting how electronic effects, lattice distortions, and spin-lattice coupling influence their phase transitions and potential for cryogenic cooling.

Contribution

It provides a comprehensive overview of the structural and magnetic behaviors of R2In compounds, integrating theoretical descriptors to predict phase stability and magnetocaloric performance.

Findings

Eu2In, Nd2In, and Pr2In exhibit giant cryogenic magnetocaloric effects.

Heavy lanthanide R2In compounds show second-order magnetic transitions.

Y2In undergoes a structural transition from hexagonal to orthorhombic near 250 K.

Abstract

R2In (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 Ni2In-type structure at room temperature, with Eu2In and Yb2In stabilizing in the orthorhombic Co2Si-type lattice. Lighter lanthanide compounds Eu2In, Nd2In, and Pr2In undergo first-order magnetic transitions with negligible hysteresis and minimal lattice volume change and exhibit giant cryogenic magnetocaloric effects, while heavy lanthanide R2In compounds including Gd2In show second-order transitions with moderate magnetocaloric effect. No lanthanide-based R2In compound exhibits symmetry-breaking structural transition, while Y2In 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