Strain and Interface Effects on Magnetocrystalline Anisotropy of MnN

Thin film effects on the Magnetocrystalline Anisotropy Energy (MAE) of MnN were studied using density functional theory (DFT). Initially, strain effects on bulk MnN were considered as a proxy for lattice-matching induced strain and a linear relationship between the c/a ratio and the MAE was found. A fundamental explanation for this relationship in terms of the underlying point-group symmetry is given, which we show is applicable to all uniaxial magnetic materials. Strain and charge-transfer effects were then considered for an ultra-thin film. It was found that a Ta seed-layer suppresses the net spin moment on the Mn ions, leading to a reduction of the MAE. Charge transfer and the associated change to the quadrupole moments of the electric field at the Mn sites is shown to be the cause of this, and hence similar effects may be expected at any magnetic heterostructure interface.