Effect of Ho on thermodynamic and magnetocaloric properties of Gd55-xHoxAl25Co20 (x=5, 10, 15, 20) metallic glasses

Liu C.; Liu B.; Ma L.; Wilde G.; Ye F.

Abstract

Gd55-xHoxAl25Co20 (x = 5,10,15,20, in at. %) metallic glass (MG) with a diameter of 5 mm were successfully fabricated. Substituting Gd by Ho improves thermal stability, manifested by respective shifts of the glass transition temperature, the crystallization onset temperature, and the peak crystallization temperature to higher temperatures. The apparent activation energies for the glass transition and for crystallization initially increase with Ho content, and then begin to decrease at higher Ho contents. All four amorphous alloys show excellent soft magnetic properties, transitioning from a ferromagnetic state to a paramagnetic state as temperature increases. Arrott curves with a positive slope indicated a second-order magnetic transition in all four MGs. Ho addition is beneficial to isothermal entropy change (|ΔSM|) and refrigeration capacity (RC), although the values of the Curie temperature and the product RC progressively decrease with increasing Ho content. Gd50Ho5Al25Co20 MG shows the best combination of magnetocaloric properties with a maximum |ΔSM| of 9.53 J·kg−1·K−1, a RC1 (the product of the peak entropy change and the full width at half maximum of the peak) of 817.77 J·kg−1, and a RC2 (integrating the area under the |ΔSM| versus temperature curves) of 674 J·kg−1 with a field change of 0–5 T (0–3980 kA·m−1).