Magnetocaloric properties of electrolytically hydrogenated La1.2Fe11.2Cr0.3Si1.5-xBx

Abstract

La1.2Fe11.2Cr0.3Si1.5-xBx (x = 0, 0.1, and 0.2) alloys were prepared and electrolytically hydrogenated for room-temperature magnetic refrigeration. It is demonstrated that electrolytic hydrogenation is as effective as thermal annealing in an H2-rich atmosphere and that boron addition can further refine the transition temperature. The addition of boron also alters the mode of the magnetic phase transition. A large peak in magnetic entropy change is observed, ranging from −14.8 J kg−1 K−1 (x = 0) to −18.5 J kg−1 K−1 (x = 0.2) at µ0∆H = 3 T, although the compositions x = 0 and x = 0.1 undergo a second-order magnetic transition (SOMT). Unlike their thermally hydrogenated counterparts, these electrolytically hydrogenated alloys are mechanically robust enough to be tested on a custom-built testbed for an extended period. In the testbed, La1.2Fe11.2Cr0.3Si1.4B0.1 generated a temperature span comparable to that of Gd at room-temperature. In addition to the material cost advantage of La over Gd, the magnetocaloric effect of La1.2Fe11.2Cr0.3Si1.4B0.1 originates from SOMT, so minimal thermal hysteresis is expected. Furthermore, the mechanical stress induced by the volume change of La(FeSi)13 during the field-induced magnetic transition can be effectively avoided, making electrolytically hydrogenated La1.2Fe11.2Cr0.3Si1.5-xBx an economical candidate for practical magnetic refrigeration at room temperature.