Strain tunability of magnetocrystalline anisotropy in Fe3GeTe2 thin films

Strain tunability of magnetocrystalline anisotropy (MCA) in Fe3GeTe2 is demonstrated for monolayer and bilayer structures. In the framework of density functional calculations, upon in-plane strain eta , -5% <= eta <= +5%, MCA exhibits contrasting behaviors for compressive and tensile strains. For tensile strain (eta > 0), perpendicular MCA is well retained with little change in the magnetic moments. For compressive strain (eta < 0), on the other hand, an abrupt decrease in E-MCA and change in the magnetic moments are prominent. It is noteworthy that bilayer Fe3GeTe2 even exhibits a sign change of E-MCA, indicating a transformation from perpendicular to in-plane magnetization. The feature of MCA is analyzed from three perspectives: (1) atomic decomposition, (2) the spin-orbit coupling (SOC) matrix in the d and p manifolds, and (3) occupation changes in the band structure. In atomic decomposition, the Te contribution predominates and accompanies a sign change in the bilayer structure. The SOC matrix in Te p manifolds under the compressive strain < m = +/- 1 , up arrow |L-z| m = +/- 1, up arrow > contribution to E-MCA > 0 decreases. In the bilayer structure, < m = +/- 1 , down arrow |L-x| m = 0, down arrow > is responsible for the sign change of E-MCA when eta = -5%.