Effect of Co substitution on thermal stability and magnetocaloric effects of Gd₇₀Al₂₀Fe_10−x Co _x amorphous alloys

The alloys with great magnetocaloric effect (MCE) are expected to be a good alternative for magnetic refrigerantion. In this work, ribbons were prepared by the melt-spinning method using Gd 70 Al 20 Fe 10− x Co x ( x = 0, 2, 4, 6, 8 and 10) alloys. Crystal structure, thermal stable, specific heat and magnetic properties of the ribbons were investigated by x-ray diffraction, Dynamic flow differential scanning calorimetry and Physical Properties Measurement System. Results show all samples are in amorphous state, and their onset crystallization temperatures (595–634 K) are higher than the magnetic transition temperature, which contributes to the stable of amorphous structures in practical application. In applied magnetic field of 5 T, the value of magnetic entropy change ∣Δ S M ∣ increases from 7.1 to 8.7 J · kg −1 · K −1 near the Curie temperature (151–114 K) of Gd 70 Al 20 Fe 10- x Co x alloys ( x = 0, 2, 4, 6, 8 and 10) , respectively, which is ascribed to the exchange interaction between magnetic atoms Co and Fe; the full width at half maximum (FWHM) of Δ S M and refrigeration capacity (RC) increase by 91% and 56% compared with those of pure Gd, respectively; the adiabatic temperature change are in the range of 3.4–3.7 K for the alloys. In addition, all alloys undergo a second order ferro-paramagnetic phase transition, which is certified by the Arrott plots and universal curves.