First principles and mean field study on the magnetocaloric effect of YFe₃ and HoFe₃ compounds

In this work, the magnetothermal characteristics and magnetocaloric effect in YFe₃ and HoFe₃ compounds are calculated as function of temperature and magnetic field. These properties were investigated using the two-sublattice mean field model and the first-principles DFT calculation using the WIEN2k code. The two-sublattice model of the mean-field theory was used to calculate the temperature and field-dependences of magnetization, magnetic heat capacity, magnetic entropy, and the isothermal change in entropy ∆S_m. We used the WIEN2k code to determine the elastic constants and, subsequently, the bulk and shear moduli, the Debye temperature, and the density-of-states at E_f. According to the Hill prediction, YFe₃ has bulk and shear moduli of roughly 99.3 and 101.2 GPa respectively. The Debye temperature is ≈ 500 K, and the average sound speed is ≈ 4167 m/s. In fields up to 60 kOe and at temperatures up to and above the Curie point for both substances, the trapezoidal method was used to determine ∆S_m. For instance, the highest ∆S_m values for YFe₃ and HoFe₃ in 30 kOe are approximately 0.8 and 0.12 J/mol. K, respectively. For the Y and Ho systems, respectively, the adiabatic temperature change in a 3 T field decreases at a rate of around 1.3 and 0.4 K/T. The ferro (or ferrimagnetic) to paramagnetic phase change in these two compounds, as indicated by the temperature and field dependences of the magnetothermal and magnetocaloric properties, ∆S_m and ∆T_ad, is a second-order phase transition. The Arrott plots and the universal curve for YFe₃ were also calculated and their features give an additional support to the second order nature of the phase transition.