Effects of strain and interface on magnetic anisotropy of FeCo/FePt: A first principles study

Using the full potential linearized augmented plane wave method, we explored the structural and magnetic properties of hybrid bilayer FeCo/FePt. The effect of interface hybridization and strain induced in FeCo by FePt buffer layer was studied. We found a tetragonal distortion in FeCo structure due to the lattice mismatch between FePt buffer layer and ferromagnetic FeCo layer. The magnetic moments of Fe and Co were insensitive to the strain effect, but the suppression in the magnetic moments of Fe and Co at the interface was observed because of the interface hybridization. The magnetocrystalline anisotropy energy of FeCo film was enhanced almost twice due to the strain. In FeCo/FePt structure, the uniaxial anisotropy constants of 9.96 and 8.78 MJ/m3 were obtained for 2 and 5 ML FeCo/FePt hybrid systems respectively. Additionally, we found that the coercive field is decreased from 146 to 119 kOe while maximum energy product increases from 74 to 85 MGOe with increase in FeCo soft layer from 2 to 5 ML. These high values of coercive field and maximum energy product may insure the basic requirement of designing rare-earth free permanent magnets.