Abstract
Using first principles calculations we studied the effect of Si substitution in the hexagonal Fe 3 Ge. We find the
low temperature magnetic anisotropy in this system to be planar and originating mostly from the spin-orbit
coupling in Fe-d states. Reduction of the unitcell volume reduces the in-plane magnetic anisotropy, eventually
turning it positive which reorients the magnetic moments to the axial direction. We find that substituting Ge
with the smaller Si ions also reduces the anisotropy, potentially enhancing the region of stability of the axial
magnetization, which is beneficial for magnetic applications. Our experimental measurements on samples of
Fe 3 Ge 1 – x Si x confirm these predictions and show that substitution of about 6% of the Ge with Si increases
by approximately 35 K the temperature range over which anisotropy is uniaxial.
