Improving Thermal Cycling Stability and Magnetocaloric Efficiency via Orbital Competition and Entropy Engineering in Rare-Earth Rhodium Indium Layered Intermetallics

A series of RE11Rh4In9 intermetallics (RE = Gd, Tb, Ho, and Tm) adopting the Nd11Pd4In9-type structure (space group Cmmm, oS48) was synthesized. The structure of these compounds has been visualized and described through CsCl- and AlB2-type fragment tiling, with the help of in-house developed software, revealing the structure as an intermediate in the CsCl- to AlB2-type structure transformation with 18% of the AlB2-type fragments and no face sharing between these fragments. Magnetic properties of RE11Rh4In9 (RE = Gd, Tb) have been examined. The compounds undergo transition from para- to ferromagnetic order near 80 K with additional magnetic transitions detectable at lower temperatures. Magnetic entropy change reaches 5.32 and 3.66 J·kg–1·K–1 under a magnetic flux density change of μ0ΔH = 0–9 T for RE = Gd and Tb, respectively. Relative cooling power and refrigerant capacity are equal to 615.4 and 501.1 J·kg–1 in Gd11Rh4In9 and 393.2 and 311.4 J·kg–1 in Tb11Rh4In9 under μ0ΔH = 0–9 T. RE11Rh4In9 establishes a structural family of Rh-containing rare-earth intermetallics that exhibit competitive magnetocaloric performance in a broad range with the maximum near 80 K. Subtle changes in the electronic structure govern exchange interactions and magnetic entropy for tuning magnetocaloric properties through controlled f–d hybridizations.