Lattice axial ratio and large uniaxial magnetocrystalline anisotropy in L10-type FePd single crystals prepared under compressive stress

L1(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 L1(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 2.1x10(7) erg/cm(3) at 4.2 K and 1.7x10(7) erg/cm(3) at 300 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 L1(0)-type Fe50Pd50 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.