Unraveling the ambient temperature magnetic cooling and critical behavior of FeCoNiCr0.63Gdx high entropy alloys

A detailed magnetocaloric and critical behavior analysis of FeCoNiCr_0.63Gd_x where, x = 0, 0.025 and 0.05 high entropy alloys (HEAs) featuring an in-depth analysis of magnetization data in the vicinity of the critical regime were studied. The critical behavior around the phase transition region is studied for both x = 0.025 and x = 0.05 compositions using various methods such as Modified Arrot plot (MAP), Kouvel-Fisher (KF) plot, and critical isotherm (CI) analysis. The positive slopes of the Arrot plots for both samples revealed that the magnetic phase transition is of second order type based on Banerjee's criterion. The critical exponents β, γ and δ estimated from the magnetic isotherms for x = 0.05 obeys the mean-field model indicating the presence of long-range spin interaction in the system. Meanwhile, the values for x = 0.025 lies within 3D-Heisenberg and Mean Field interaction models which shows the weakening of the long-range interactions and the existence of magnetic inhomogeneity within the system. Furthermore, the variation of effective critical exponents (β_eff and γ_eff) with temperature for x = 0.025 sample is reminiscent of disordered ferromagnetic system. It is rather significant that the scaling laws are satisfied suggesting the renormalization of interactions near T_C. A maximum entropy change of ΔS_m = 1.09 Jkg⁻¹K⁻¹ and 1.22 Jkg⁻¹K⁻¹ (x = 0.025 and 0.05) and a substantial relative cooling power (RCP) of 39.21 Jkg^-1 and 104.75 Jkg⁻¹ were observed for varying magnetic field of 70 kOe. Given the notable RCP and tuneable T_C near the ambient temperature, the as studied HEAs could be an eminent candidate for magnetic refrigeration applications.