Pressure-induced mechanically, thermodynamically and structurally stable half-metallic ferromagnetic NiSc2X4 (X = S and Se) spinels for spintronic applications: DFT-calculations.

Spintronics represents an area of study that makes use of the spin characteristic of the electron to control the behavior of quantum electronics devices relative to the typical charge electronics. In the present study, we carried out a detailed density functional theory-based analysis on the thermodynamic and mechanical stability of half-metallic ferromagnetic NiSc2X4 (X = S and Se) spinels under the influence of pressure. The formation energies and energy minimization in both the ferromagnetic and antiferromagnetic arrangements confirm the energetic stability in the ferromagnetic state. Also, there are no imaginary frequencies in the phonon dispersion and ab initio molecular dynamics simulations, showing that these two compounds are dynamically stable. It is clear that the mechanical behavior of these two materials is quite stable since they exhibit high Poisson's ratios and high bulk-to-shear modulus ratios. The Poisson's ratios of NiSc2S4 and NiSc2Se4 are found to be 0.309 and 0.295, respectively. The B0/G ratios of NiSc2S4 and NiSc2Se4 are found to be 2.287 and 2.114, respectively. Analysis of the electronic properties indicates that an increase in the applied pressure from 0 GPa to 4 GPa leads to a significant reduction in the direct band gap. Most importantly, NiSc2S4 becomes a half-metallic ferromagnet under increased pressure. The magnetic calculations indicate a magnetic moment of 2.00 µ B per formula unit for both NiSc2S4 and NiSc2Se4, which originates mainly from the Ni atom. Also, an analysis of the thermodynamic properties of these two compounds, using the quasi-harmonic Debye approximation as implemented in the GIBBS2 program, shows lattice stiffening, phonon softening, and anharmonicity effects. The calculated entropy and Debye temperatures further confirm the stability and vibrational integrity of the system. Overall, these results show the potential of NiSc2X4 spinels in spintronic and magneto-electronic devices.