Influence of 5d transition elements on the magnetocrystalline anisotropy of hcp-Co

We have studied the effects of 5d transition elements (X = W, Re, Ir, and Pt) on the magnetocrystalline anisotropy energy (MAE) of epitaxially grown hexagonal-close-packed (hcp)Co (1010) single crystal films. The MAE of Co-X significantly changes, depending on X. With increasing numbers of valence electrons in X, the sign of the first anisotropy constant KI changes from positive to negative, indicating that the easy axis of magnetization rotates from the c-axis to the c-plane. The second anisotropy constant K-2 monotonically increases with the number of valence electrons in X. All these variations were found to be systematic and are discussed in conjunction with the structural analyses.