Compositionally complex alloying in multiple-R-Co₂ laves phase system: Lattice distortion and static and dynamic magnetocaloric properties

Compositionally complex (CC) alloying strategies can improve performance under operational conditions as demonstrated by the advancements of high-entropy alloys but their effect on the thermomagnetic functionality remains unclear. The findings of this work reveal the CC effects on thermomagnetic functionality by systematically investigating CC alloying at the rare-earth (R) site of the RCo₂ system, particularly focusing on both static and dynamic magnetocaloric effects. By combining Tb, Dy, Ho, Er and Gd elements in near-equiatomic proportions (which increases the configurational entropy of mixing), significant isothermal entropy changes, akin to those observed in the well-known DyCo₂, are found across a broad temperature span, indicating the potential for multi-stage coupling applications. Exponent n analysis indicates the series is near the critical composition, enabling substantial responses without thermal hysteresis. Direct measurements of the adiabatic temperature change of Dy_0.25Tb_0.25Ho_0.25Er_0.25Co₂ show that CC alloying at the R-site does not decrease cyclic performance at frequencies below 5 Hz in alternating magnetic fields with respect to DyCo₂. High-resolution electron micrographs and variable temperature X-ray diffraction results reveal a 39.5 % increase in lattice distortion compared to DyCo₂, raising the phase transition energy barrier from 0.28 to 0.47 eV. These findings shed insights into the dynamic thermomagnetic responses and underscore the potential of CC alloying to improve the magnetocaloric effects of RCo₂ family.