FIRST-PRINCIPLES CALCULATION OF THE MAGNETOCRYSTALLINE ANISOTROPY ENERGY FOR THE PSEUDOBINARY COMPOUND Y(Co1−xFex)5

From the experimental behavior of the magnetocrystalline anisotropy energies of the pseudobinary compounds Y(Co1−xFex)5, it has been argued that the magnetocrystalline anisotropy energies for YCo5 and the hypothetical compound YFe5 will have different signs. This anomalous behavior is attributed to the change of the number of 3d electrons and their orbital moments when proceeding from YFe5 to YCo5. The magnetocrystalline anisotropy energies are calculated using the linear muffin-tin orbital (LMTO) method in the atomic sphere approximation (ASA) including spin-orbit interaction and orbital polarization. The force-theorem is used to express the total energy difference (between the two directions of magnetization) as a difference in the sum of the single particle eigenvalues. We find that it is possible to predict the correct easy-axis for YCo5 and YFe5. Secondly it is found that the inclusion of orbital polarization is essential for the cobalt compound but less important for the iron compound. The different contributions from the two inequivalent transition metal sites to the anisotropy energy and orbital magnetization are discussed.