First-principles investigations of the electronic structure and magnetocrystalline anisotropy in strained magnetite Fe3O4

The electronic structure and magnetocrystalline anisotropy energy of strained fcc Fe3O4 have been studied by using the linear muffin-tin orbital method within density functional theory. A uniaxial strain applied along the [001] direction of the magnetite is considered. It is found that the applied strain would initially reduce the calculated band gap of the majority spin and then turn the half-metallic behavior in the cubic limit into the normal metallic state at high in-plane strains of -1.3% and 2.1%. The calculated fourth-order anisotropy constant K-1 of cubic Fe3O4 is in fair agreement with the experimental value. The magnitude of K-1 appears to be suppressed under large extensive lateral strains. The second order uniaxial anisotropy constant K-out is positive for extensive in-plane strains and is negative for compressive in-plane strains. The positive value of K ut minus the shape anisotropy indicates that an Fe3O4 film under an extensive in-plane strain larger than 0.2% would show the perpendicular magnetization, in good agreement with recent experiments on Fe3O4 films on MgO(100) and CoO(100). Interestingly, site decomposition shows that the A- and B-site Fe atoms in the strained magnetite have comparable anisotropy energies but with the opposite signs. while the oxygen's contribution is negligible. This implies that under an extensive lateral strain, the B-site irons would favor perpendicular magnetization while the A-site irons would prefer an in-plane magnetization. The total K-out is dictated by that of the B-site irons due to their number being twice that of the A-site irons.