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 Dy0.25Tb0.25Ho0.25Er0.25Co2 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.

This work was supported by the Science Center of the National Science Foundation of China (52088101), the National Key R&D Program of China (2023YFA1406003, 2020YFA0711500, 2021YFB3501202), the National Natural Science Foundation of China (U23A20550, 92263202, 22361132534) and the Strategic Priority Research Program B (XDB1270201) and the key programs of Chinese Academy of Sciences. The study was also supported by the Russian Science Foundation, Grant No. 24–43–00156, and the NSFC, Grant No.2231101520. JYL, LMMR and VF acknowledge Grants PID2019–105720RB-I00 and PID2023–146047OB-I00 funded by MCIN/AEI/ 10.13039/501100011033, the Clean Hydrogen Partnership and its members within the project HyLICAL (Grant No. 101101461), the Research Council of Norway within the project LIQUID-H, project PPIT2024–31833, co-financed by EU, Ministerio de Hacienda y Función Pública, FEDER, and Junta de Andalucía, and VII Plan Propio de Investigación from University of Seville. JYL and VF acknowledge the support of Chinese Academy of Sciences President’s International Fellowship Initiative (PIFI) for visiting scientists (Grant No. 2024VMA0021, 2024VMC0006). JYL acknowledges EMERGIA 2021 fellowship from Junta de Andalucía (Ref. EMC21_00418).

Peer reviewed