Thin films of itinerant-electron ferromagnets on a nonmagnetic metallic substrate

We report a simple theory of a film, no more than a few atoms thick, of an itinerant ferromagnet deposited on a semi-infinite nonmagnetic metallic substrate. The magnetic properties of such a film are described by the use of Hubbard's model Hamiltonian for a narrow $s$ band and the substrate is represented as an uncorrelated $s$-band metal. The screened, single-site interaction term in Hubbard's Hamiltonian is decoupled in the Hartree-Fock approximation. Consequent to this description, the magnetic moments in those layers of the film immediately adjacent to the interface are found to be strongly dependent on the value chosen for the nearest-neighbor transfer-matrix element connecting the film and the substrate. For the case when the film is a monatomic layer, its moment is found to disappear altogether if that transfer-matrix element is sufficiently, yet not unreasonably, large. Furthermore, the moment is found to vanish much more readily for films which have a nearly filled band (as in nickel) than for those with an approximately half-filled band (as in iron). In thicker films, the lowest one or two layers have essentially similar properties. Overall, this theory leads to results which agree reasonably well with the recent observations of Bergmann upon films of nickel, cobalt, or iron on the nonmetallic substrate ${\mathrm{Pb}}_3$Bi.