Electric field assisted magnetization reversal in FePt films.

We propose to use strain assisted reduction in anisotropy of FePt in order to make magnetization reversal easier in the writing of the magnetic storage devices. We performed first-principles calculations of the magnetocrystalline anisotropy of FePt under bi-axial stress using full-potential LAPW implemented in FLEUR code. Magnetocrystalline anisotropy decreases by 25{\%} with application of 1.5{\%} tensile biaxial strain. This is partially due to the reduction of the c/a ratio by about 1.5{\%} (calculated Poisson ratio is 0.33) in the tetragonal cell and partially due to the increase in volume by about 1.5{\%}. Biaxial strain can be obtained by placing piezoelectric film under FePt layer, and by applying electric field on the system. Modern ferroelectric systems can provide stress up to 2{\%}. Besides, we propose using thin ferroelectric films with asymmetric interfaces, which provides a simple way to generate bias field in the polarization reversal and related properties. The existence of the polar interfaces results in a different average polarization in the film upon reversal. As a result, the strain in the film depends on the direction of polarization. This asymmetric strain can be used do modulate magnetic properties.