ORBITAL MAGNETISM AT THE SURFACES OF 3D TRANSITION-METALS

The local orbital magnetic moments L-delta(i) at different layers i cl ose to the surfaces of Fe, Co, and Ni are determined in the framework of a d-band Hamiltonian, which includes hybridizations, Coulomb intera ctions, and spin-orbit coupling on the same electronic level. Differen t directions of the magnetization delta are considered in order to qua ntify the anisotropy in L. For each delta, the spin-polarized charge d istribution and the local densities of states from which L is derived an calculated self-consistently. The role of the local atomic environm ent is investigated by performing calculations on the (001), (110), an d (111) surfaces of the bcc, hcp, and fcc lattices. L-delta(i) is sign ificantly enhanced at surface atoms as compared to the corresponding b ulk moment L-delta(bulk). L depends strongly on the local coordination number and is generally larger the mere open the surface is. For exam ple, for the Fe(001) surface L-x(1)L-x(bulk) = 2.2 and for the Fe(110) ) surface L-x(1)/L-x(bulk) = 1.3. L-delta(i) decreases abruptly as we move from the uppermost layer (i=1) to the second layer (i = 2). After some oscillations, convergence to L-delta(bulk) is reached quite accu rately for i greater than or equal to 6. The largest anisotropy in L-d elta(i) is found at the hcp (0001) surface of Co (L-parallel to - L-pe rpendicular to similar or equal to 0.02 mu(B)). The orbital moments at purl surfaces are compared with results for deposited films by consid ering four layers of Co on Pd(111) as a representative example.