First principles and mean field study on the magnetocaloric effect of YFe3 and HoFe3 compounds Mohammed Said Mohammed Abu-Elmagd, Tarek Hammad, Ahmed Abdel-Kader, Nesreen El-Shamy, Sherif Yehia, et al. Scientific Reports, 2023 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 ∆Sm. 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 Ef. 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 ∆Sm. For instance, the highest ∆Sm 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, ∆Sm and ∆Tad, 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.
Density functional theory (DFT) calculations of structural, elastic, and thermal properties of Zn3P2compound T. R. Hammad International Journal of Modern Physics B, 2023 In this paper, theoretical investigations of structural, elastic and thermal properties of Zn3P2 material were done using Quantum ESPRESSO code based on density functional theory. The generalized gradient approximation (GGA) exchange correlation-functional helped to model the atomic interaction. First, the structural optimization procedure was carried out, and hence, the optimized structural parameters were utilized to obtain six independent elastic constants [Formula: see text], and [Formula: see text] for the Zn3P2 tetragonal structure. Accordingly, these elastic constants were used to determine the elastic moduli such as the Bulk modulus, Young’s modulus, and shear modulus, as well as other mechanical parameters such as Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities and Debye temperature. Calculations of thermodynamic properties such as vibrational energies, vibrational free energies, and fixed volume heat capacities, were performed within the implementation of the Thermo_pw code. Elastic calculations confirmed that this compound is characterized by mechanical stability at zero pressure and 0K temperature, ionic bonding, a high degree of anisotropy, and typical ductility. An observable increase in Debye vibrational energies, entropies and constant volume heat capacities of this compound with increasing temperature was detected throughout the thermodynamic calculations, unlike vibrational free energy which revealed a pronounced decrease as temperature increased.
