Electronic band structure, phase stability, magnetic and thermoelectric characteristics of the quaternary Heusler alloys CoCuZrAs and CoRhMoAl: Insights from DFT computations

The search for new materials with stable structures and unique functional properties is important for the development of future technologies. Herein, by performing first-principles calculations based on density functional theory (DFT), we have explored two new quaternary Heusler alloys, CoCuZrAs and CoRhMoAl. The total energy calculations reveal that CoCuZrAs (CoRhMoAl) is stable in the Y2 (Y1)-type structure among the three possible atomic configurations and that both alloys are ferromagnetic in the ground state. Electronic properties computed at the GGA level show that the present alloys have metallic behavior, whereas CoRhMoAl is a half-metal at GGA + U (U ≥ 1 eV) due to the opening of a band gap at the Fermi level in the spin-down channel. Furthermore, CoRhMoAl retains its half-metallicity when pressure is applied (in the range of 0–25 GPa). The magnetic data reveal that CoCuZrAs has a total spin moment of 2.34 µ_B, whereas CoRhMoAl has an integral spin moment of 3.0 µ_B, which is in line with the Slater-Pauling formula M_t = Z_t-24 (where M_t = total spin moment/cell, Z_t = total valence electrons/cell). In CoCuZrAs, the Co, Cu, Zr and As atoms contribute individual spin moments of 2.16 µ_B, −0.03 µ_B, 0.18 µ_B and 0.04, respectively, whereas in CoRhMoAl, the Co, Rh, Mo, and Al atoms carry spin moments of 1.81, 0.17, 1.14 and −0.09 µ_B, respectively. These results are also supported by the corresponding spin density plots, where the spin density is mainly located at Co atoms. The thermoelectric properties calculated up to 1000 K exhibit interesting features that might be useful in energy production.