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 P t) on the magnetocrystalline anisotropy energy (MAE) of epitaxially grown h exagonal-close-packed (hcp)Co (1010) single crystal films. The MAE of Co-X significantly changes, depending on X. With increasing numbers of valence e lectrons in X, the sign of the first anisotropy constant KI changes from po sitive to negative, indicating that the easy axis of magnetization rotates from the c-axis to the c-plane. The second anisotropy constant K-2 monotoni cally increases with the number of valence electrons in X. All these variat ions were found to be systematic and are discussed in conjunction with the structural analyses.