Search for half-metallicity in new ferrimagnetic quaternary MnXMoAl (X= Co and Ti) Heusler alloys: A DFT based investigation

Highly spin-polarized magnetic materials emerge as promising candidates for spintronic technology. Herein, we present a theoretical study of two new equiatomic quaternary Heusler alloys MnCoMoAl (MCMA) and MnTiMoAl (MTMA) in LiMgPdSn-type structure. On performing volume optimization in three possible Y-type structures, it is confirmed that the MCMA (MTMA) alloy is stable in Y₁ (Y₂)-type structure. The magnetic moment data reveals that alloys are ferrimagnetic (FIM) in the ground state. It is shown that MCMA is a highly spin-polarized (88.24%) metal, whereas, MTMA exhibits complete half-metallic properties with 100% spin-polarization and a band gap of about 0.20 eV in the spin-down channel at the Fermi level. Besides, MCMA carries a total magnetic moment of 0.92 μ_B whereas MCMA has an integral spin magnetic moment of ~2.0 μ_B. It is found that the largest moment is contributed by Co (Mn) atoms in MCMA (MTMA). To examine the effect of uniform strain on the magnetic properties, the total moment is calculated as a function of strain. It is noticed that the total moment of the alloys does not change significantly when strain is applied in the range −12%–12%. In addition, the effect of temperature and pressure on the thermodynamic properties has been examined. The coefficient of thermal expansion (α) and specific heat capacity (C_V) increase (decrease) with increasing temperature (pressure). The Gru¨neisen parameter and Debye temperature remain almost unchanged when temperature varies from 0 K to 900 K. The proposed materials may have applications in future spintronics.