Material-specific mechanism of uniaxial magnetic anisotropy in transition metal alloys

Magnetocrystalline anisotropy in six transition metal alloys, FePt, CoPt, FePd, MnAl, MnGa, and FeCo, was studied using first-principles calculations to elucidate the specific mechanism. The tight-binding linear muffin-tin orbital method in the local spin-density approximation was employed to calculate the electronic structure of each compound, and the anisotropy energy was evaluated using the magnetic force theorem and second-order perturbation theory in terms of the spin-orbit interactions. We systematically described the mechanism of uniaxial magnetic anisotropy in real materials and presented the conditions under which the anisotropy energy can be increased. The large magnetocrystalline anisotropy energy in FePt and CoPt arises from the strong spin-orbit interaction of Pt. In contrast, the anisotropy energy of MnAl, MnGa, and FeCo is comparable with that of FePd. We found that MnAl, MnGa, and FeCo satisfy the condition efficiently, even though the spin-orbit interaction is weak. These compounds have an electronic structure that is favorable for inducing anisotropy in the energy variation when the magnetization is aligned in a particular direction in the crystals.