Strain Dependent Magnetocrystalline Anisotropy from First Principles*

There has been emerging interest in metallic antiferromagnets since the potential for electrical switching was shown for CuMnAs and Mn$_2$Au. Magnetocrystalline anisotropy (MCA) is essential to understand spin dynamics and strain can be utilized to modify the anisotropy energy.

We used first-principles density functional theory to compute the strain dependence of MCA for Fe$_2$As and Mn$_2$As, which have same magnetic structure as CuMnAs.

The out-of-plane MCA of both materials is about 100 times larger than in-plane MCA. We then applied bi-axial strain on Mn$_2$As and uni-axial strain on Fe$_2$As to simulate directional strain in thin films. From this we show a tendency to decrease MCA under tension. Reduction of out-of-plane MCA was 3\% for 0.3\% strained Mn$_2$As and 30\% for 2\% strained Fe$_2$As. For Fe$_2$As, 2\% uni-axial strain distorted tetragonal unit cell into orthorhombic and the in-plane MCA became 100 times larger compared to the unstrained MCA.

Further investigation with larger range of strain would map the correlation between strain and energy to decide general amount of strain that can optimize MCA for device applications in the studied materials.