Effective electron-density dependence of the magnetocrystalline anisotropy in highly chemically ordered pseudobinary (Fe1-xMnx)50Pt50 L10 alloys

The magnetic and structural properties of highly chemically ordered epitaxial (Fe1-xMnx)(50)Pt-50 (0 <= x <= 0.68) thin films were investigated. This study complements earlier experimental studies on pseudobinary ternary and quaternary FePt-based alloys, providing a more complete picture of the dependence of the magnetization and magnetocrystalline anisotropy on structural properties and effective electron density in the chemically ordered 3d transition metal-Pt L1(0) alloy system. Maximum anisotropy and magnetization are found for the undoped FePt composition, and increasing Mn additions result in a steady reduction of magnetocrystalline anisotropy and saturation magnetization. Comparing the results of our experimental study to two recent computational first-principles studies of pseudobinary L1(0) alloys, we find a significantly more rapid reduction of magnetization and anisotropy with decreasing effective electron density than predicted by either of the two theories. This reduction may be explained in part by the antiparallel alignment of Fe and Mn moments observed in circular x-ray magnetic dichroism.