Lattice axial ratio and large uniaxial magnetocrystalline anisotropy inL10-type FePd single crystals prepared under compressive stress

Abstract

$L{1}_{0}$-type FePd single crystals with a high order degree were prepared by ordering under compressive stress. Experimental and theoretical investigations on the relation among the axial ratio, $d$ electron number and magnetocrystalline anisotropy energy (MAE) in $L{1}_{0}$-type FePd single crystals have been carried out. In the concentration dependence of the lattice constants, the $a$ axis exhibits a strong dependence, compared with that of the $c$ axis. As a result, the ratio of $c∕a$ decreases with increasing Pd concentration. The uniaxial magnetocrystalline anisotropy constant ${K}_{U}$ at the equiatomic composition is evaluated to be $2.1\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $1.7\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The MAE becomes weaker as the ratio of $c∕a$ is apart from unity at higher Pd compositions. The calculated results by the first principles calculations with the LMTO-ASA including the spin-orbit coupling for the MAE of $L{1}_{0}$-type ${\mathrm{Fe}}_{50}{\mathrm{Pd}}_{50}$ are in accord with the present experimental results. The increase in the $d$ electron number due to the increase of the Pd concentration facilitates the decrease of the MAE, cooperating with the decrease in the axial ratio $c∕a$.