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

$L{1}_0$-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 $2.1\times {10}^7\mathrm{erg}∕{\mathrm{cm}}^3$ at $4.2\mathrm{K}$ and $1.7\times {10}^7\mathrm{erg}∕{\mathrm{cm}}^3$ at $300\mathrm{K}$. 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 $c∕a$.