Effect of Cu on thermal and magnetocaloric properties of (GdTbHo)CoAl high-entropy metallic glasses

(Gd1/3Tb1/3Ho1/3)55Co17.5Al27.5-xCux (x = 5, 10, 15, and 20) metallic glasses (MGs) with a high configurational entropy (Delta Sconf) of 1.723-1.754 R were successfully prepared by arc melting technology. Their glass-forming ability (GFA), thermodynamic behavior, and magnetocaloric effect (MCE) upon Cu addition were investigated thoroughly. Upon Cu addition, both Tg and the Tx significantly decrease with increasing 3d electron number due to the weakened f-d hybridization effect. The (Gd1/3Tb1/3Ho1/3)55Co17.5Al12.5Cu15 with 15 at. % Cu exhibits a maximum value of GFA criteria, including Trg, gamma, and gamma m, as well as the lowest degree of structural order, indicating its optimal GFA, which is likely associated with the high-entropy effect and suppressed crystallization behavior. Moreover, it is found that the refrigeration capacity (RCP) also reaches a peak value of 624.83 J kg-1 with a relatively larger peak magnetic entropy change (|Delta Spk ) of 8.75 J kg-1 K-1 at the composition with 15 at. % Cu, accompanied by an abnormally high Curie temperature (TC) of 59 K, which is attributed to the high experimental mu eff of (Gd1/3Tb1/3Ho1/3)55Co17.5Al12.5Cu15 as a result of the intensified magnetic interaction between rare-earth (RE) elements for alloying Cu with small size. Our work indicates that Cu is an effective element for manipulating the thermal and magnetic properties of magnetocaloric materials by influencing their microstructure, orbital hybridization effects, and magnetic exchange interactions.