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 f unction of the bond length for the Fe, cluster. In particular it is sh own that the MAE may be qualitatively related to the projections of th e orbital moment along the magnetization directions, and that the ''in -plane'' anisotropy can be of the same order of magnitude as the ''per pendicular'' anisotropy. Using the same Hamiltonian, the problem of th e convergence of the magnetic anisotropy energy of very thin films is revisited. By the choice of a basis which mixes spherical harmonics, i t is shown that the irregular oscillations of the MAE versus the band filling disappear. For Co(111) excellent stability of the in-plane ani sotropy as observed experimentally was found. Finally, the crystal-fie ld effects are also discussed.