Cryogenic magnetocaloric performance in single-crystalline Er1−xTmxAl2(x=0,0.1,and0.3)

Abstract

The development of highly efficient, solid-state refrigerants operating near the hydrogen liquefaction temperature (T≤20.5K) is crucial for next-generation cryogenic cooling. This study addresses a critical gap in the field by synthesizing and characterizing high-purity, single-crystalline ErAl2 and Er1−xTmxAl2 (x=0.1and0.3) via the metal flux method. While previous work has been limited to polycrystalline forms, the use of single crystals provides essential insights into intrinsic magnetic properties, specifically magnetic anisotropy. ErAl2 single crystals exhibit ferromagnetic ordering at Tc≈10.5K, revealing a strong magnetic anisotropy where the < 111 > direction is the magnetic easy axis. This anisotropy leads to a highly direction-dependent magnetocaloric effect (MCE). Along the easy axis, the maximum isothermal entropy change (∆Sm) for ErAl2 reaches 24.9J/kg·K for a field change of 20kOe. Furthermore, the < 100 > and < 110 > directions exhibit a spin reorientation near 7K. Crucially, Tm substitution significantly enhances the MCE performance along the easy axis, with Er0.7Tm0.3Al2 achieving a record-high ∆Sm of 27.1J/kg·K (ΔH=20kOe) among materials operating in this cryogenic range. The maximum rotational magnetic entropy change (∆Sr) of 18.3J/kg·K for ErAl2 at 20kOe demonstrates its competitive performance for rotational refrigeration applications. These results confirm that the Er1−xTmxAl2 single crystal, particularly along the <111> direction, is a promising candidate for cryogenic magnetic refrigeration application relevant to hydrogen liquefaction. © 2026