Strain control of magnetocrystalline anisotropy and energy product of MnGa alloys

We investigate the energy product of MnGa alloys as function of Mn concentration and applied elastic strain. Using the density functional theory (DFT) based method we calculated the magnetocrystalline anisotropy (MAE) and magnetization of Mn–Ga alloys as function of composition, e.g. Mn and Ga, and examined their variation under applied strain. Our calculations show that MAE is very large ~22–27 M erg/cm³ in all three considered compositions, e.g. MnGa, Mn₃Ga and Mn_1.66Ga. We show that MAE is very robust in MnGa system and remains large in wide range of concentrations and strains both compressive and tensile. We find that bi-axial tensile strain increases MAE in Mn_1.66Ga alloys. Our study shows that the variation of MAE as function of Mn content is related to the change in electronic structure and, specifically, the Fermi level position with electron population variation. We estimated the theoretical limit of the energy product (BH)_max of MnGa, Mn₃Ga and Mn_1.66Ga alloys as 23.65, 4.06 and 13.64 MGOe, respectively. We find that volume expansion of the MnGa alloys (by appropriate doping) should increase the magnetization and the energy product of these alloys