Highly spin-polarized electronic structure and magnetic properties of MnCoAl Ge Heusler alloys: first-principles calculations.

Highly spin-polarized half-metals (HMs) and spin-gapless semiconductors (SGSs) are the promising candidates in spintronic devices. However, the HM and SGS Heusler materials are very sensitive to the stoichiometric defects and lattice distortion, which will be not beneficial to the practical applications. Here, the electronic structure and magnetic properties of MnCoAl Ge ( = 0, 0.25, 0.50, 0.75 and 1.00) Heusler alloys were investigated by first-principles calculations. Large negative formation energy, cohesive energy and phonon spectra confirm that the MnCoAl Ge alloys are stable. It is found that MnCoAl Ge with = 0, 0.25, 0.75 and 1.00 show robust ferrimagnetic HM characteristics, while MnCoAlGe shows robust SGS characteristic. Under the hydrostatic and uniaxial strains, MnCoAl Ge exhibit a series of rich electronic transitions. The magnetic anisotropy of MnCoAl Ge turns from the in-plane [100] direction to the out-of-plane [001] one by applying the uniaxial strains. The results suggest that the complete spin polarizations of MnCoAl Ge alloys are robust against the stoichiometric defects and lattice distortion, which have potential applications in spintronic devices.