Strain-induced control of magnetocrystalline anisotropy energy in FeCo thin films

Highlights: • Lateral strain can be used to tune the magnetocrystalline anisotropy of thin FeCo films. • Magnetostriction may be minimized if the strain derivative of the anisotropy is zero. • The thickness and surface orientation of the slabs significantly changes the anisotropy. • Fully ordered ${\mathrm{Fe}}_{50}{\mathrm{Co}}_{50}$ slabs show significantly different strain dependence of the magnetic anisotropy than disordered ${\mathrm{Fe}}_{10}{\mathrm{Co}}_{90}$ slabs. We use density functional theory calculations to compute the lateral strain dependence of the magnetocrystalline anisotropy (MCA) energy of thin FeCo films. We investigate the effect of lateral strain on the MCA energy especially in the context of magnetostriction, which needs to be minimized for some applications like GMR sensors. The magneto-elastic coupling responsible for magnetostriction is a strain-derivative of the MCA energy, thus we concentrate to find extrema in the MCA energy vs. strain curves, which we find for both ordered ${\mathrm{Fe}}_{50}{\mathrm{Co}}_{50}$ films, as well as for disordered ${\mathrm{Fe}}_{10}{\mathrm{Co}}_{90}$ films modeled by special quasirandom structures. We show that using lateral strain we can switch the easy axis of magnetization from out-of-plane to in-plane in many cases. We can furthermore use lateral strain in combination with the film-thickness to minimize magnetostriction and change the MCA energy at the same time.