Structural, Electronic, Elastic, And Thermodynamic Properties Of The Spin-gapless Semiconducting Mn₂CoAl Inverse Heusler Alloy Under Pressure

With the development of spintronics, the Half-metallic ferromagnets(HFMs) have attracted a mount of attention in recent years. Half-metallic magnets present metallic behavior for one spin channel, while there exists a gap for the other spin one, thus creating 100% spin-polarization current in devices. This feature is of great importance in spin-dependent device such as tunnel junctions, spin-injection, spin-filters, and giant magnetic resistance(GMR) devices.Since the half-metallicity of the half-Heusler alloy Ni Mn Sb was first predicted theoretically by de Groot et al using the first-principles calculations in 1983, more and more half-Heusler and Heusler alloys have been verified to possess such half-metallicity and been classified into half-metallic ferromagnets(HMFs). During these two decades, much attention has been paid to Heusler alloys owing to its Curie temperature and magnetic moment. In particular, several of the inverse Heusler compounds such as Mn2 Co Al and quaternary Heusler alloys such as Co Fe Cr Al have been recently identified to be spin-gapless semiconductors, namely, there is an energy gap in the minority spin channel around the Fermi level, while the conduction- and valence-band edges of majority electrons touch at the Fermi level. In the spin-gapless semiconductors, the mobility of carriers is stronger than that in regular semiconductors, and not only the electrons but also the holes can be completely spin polarized. Also, no threshold energy is required to excite electrons from the valence band to the conduction band. We extensively investigate the structural, electronic, elastic, and thermodynamic properties of the spin-gapless semiconducting Mn2 Co Al under pressure based on first-principles calculations and the quasi-harmonic Debye model.In details, the main results of our studies are summarized as follows:1. To obtain the ground-state structure of Mn2 Co Al, we first calculate the total energy by varying the volume. The calculated E–V data are fitted to the third-order Birch–Murnaghan equation of states, thus the equilibrium lattice constant0 a, bulk modulus0 B, and its pressure derivative 0B￠ are obtained. It can be clearly seen that the calculated structural parameter is in excellent agreement with the available experimental and theoretical data, suggesting the reliability of the present calculations.2. In order to examine if the spin-gapless semiconductors behavior is also presented under pressure, we explore the band structure and total density of states around the Fermi level. It shows that spin-gapless semiconductors behavior of Mn2 Co Al is robust against pressure less than 25 GPa in everyday experiments.3. After checking all the independent elastic constants under different pressures satisfy the generalized elastic stability criteria, we conduct the Voigt–Reuss–Hill(VRH) approximation to obtain other mechanical properties, such as bulk modulus B, Young’s modulus E, and the shear modulus G. It becomes increasingly difficult to compress Mn2 Co Al as pressure increases. And Mn2 Co Al becomes more and more ductile with increasing pressure up to 25 GPa.4. Based on first-principles calculations and the quasi-harmonic Debye model, we calculate the thermodynamic properties, such as thermal expansivity a, Grüneisen parameter γ, heat capacity C_V, and Debye temperature (?)_D, of the spin-gapless semiconducting Mn2 Co Al are evaluated to 25 GPa.