Co$_2$MnZ (Z = Al, Si, Ga, Ge, Sn) Heusler alloys as candidate materials for spintronic and microelectronic applications: Electronic structure, transport, and magnetism

Abstract

Magnetic and electronic transport properties of Co$_2$MnZ (Z = Al, Ga, Ge, Si, Sn) Heusler alloys were experimentally investigated. Electrical resistivity, in the temperature range from 4.2 to 300 K, as well as field dependences of the Hall effect and magnetization at T = 4.2 K in magnetic fields up to 100 kOe and 70 kOe, respectively, were measured. Experimental data are in good agreement with the results of the theoretical DFT calculations of the electronic structure and magnetic moments. In the band structure of Co$_2$MnSi, half-metallicity is formed with the full spin polarization and the half-metallic gap of about 0.6 eV. In Co$_2$MnZ (Z = Al, Ge, Sn), it is shifted from the Fermi energy by the hole pockets at the point $\Gamma$, preventing thereby the formation of the half-metallic state. In a peculiar case of Co$_2$MnGa, the antisite defects are expected to determine structural and electronic properties. For the Co$_2$MnAl and Co$_2$MnGa topological semimetals, Weyl topological points are found at the Fermi energy; however, for Z = Si, Ge, Si, these features are located deeper within to the valence band. The results show that Co$_2$MnGe and Co$_2$MnSn are usual ferromagnets, Co$_2$MnAl and Co$_2$MnGa alloys are topological semimetals that can find application in microelectronics, while Co$_2$MnSi is a half-metallic ferromagnet that is in high demand in spintronics.