MAGNETIC-ANISOTROPY OF SMALL CLUSTERS AND VERY THIN TRANSITION-METAL FILMS

The magnetic anisotropy of 3d-TM clusters is studied in the framework of a d-electron tight-binding Hamiltonian including hopping, Coulomb, and spin-orbit interactions on the same electronic level. Results for the magnetic anisotropy energy and spin-polarized DOS are given as a function of the bond length for the Fe6 cluster. In particular it is shown that the MAE may be qualitatively related to the projections of the orbital moment along the magnetization directions, and that the"in-plane" anisotropy can be of the same order of magnitude as the"perpendicular" anisotropy. Using the same Hamiltonian, the problem of the convergence of the magnetic anisotropy energy of very thin films is revisited. By the choice of a basis which mixes spherical harmonics, it is shown that the irregular oscillations of the MAE versus the band filling disappear. For Co(111) excellent stability of the in-plane anisotropy as observed experimentally was found. Finally, the crystal-field effects are also discussed.