First-principles study of magnetic properties of L10-ordered MnPt and FePt alloys

Using first-principles methods, we study the magnetic and electronic properties of three different spin configurations of the L1(0) phase of FePt and MnPt alloys. It is found that MnPt and FePt may be approximately considered as magnetic antipodes with opposite ferromagnetic (FM)-antiferromagnetic (AFM) and in-plane/ out-of-plane magnetocrystalline anisotropy (MCA) relationships. In MnPt, the most stable phase is the AFM configuration with AFM chessboard spin coupling in the (001) plane, FM spin coupling between (001) planes, and all spin directions aligned in the (001) plane. Whereas in FePt, the most stable is the FM configuration with all spin directions aligned perpendicular to (001) plane. The out-of-plane MCA of MnPt is more than an order of magnitude less (similar to 0.1 meV) than that of FePt (similar to 2.9 meV) in their corresponding magnetic ground states. Our calculations indicate that an AFM state can be achieved in FePt by a small variation in tetragonality ratio (from 0.98 to 0.94). A pseudogap is observed at the Fermi energy for MnPt and just below the Fermi energy for FePt for the chessboard AFM model. This pseudogap may explain the ground-state magnetic configuration of MnPt.