Spin-Polarization in Ultrathin Rh Layers on Fe(001)
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SPIN-POLARIZATION IN ULTRATHIN Rh LAYERS ON Fe(001) A. CHOUAIRI*. H. DREYSSE *, H. NAIT-LAZIZ** AND C. DEMANGEAT** *Laboratoire de Physique de Solide, BP 239, 54506 Vandoeuvre-les-Nancy, France. **IPCMCS, Universit6 Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg, France. ABSTRACT The origin of the Rh polarization at the interface with Fe is discussed within a selfconsistent mean-field parameterized tight-binding model. Since experimentally it is not yet known how Rh grows on Fe(001), in this paper we consider both fcc and bcc growth. When Rh grows in the fcc structure, it expands its lattice parameter and a polarization is present up to 3 layers, whereas in the bcc case only the Rh atoms at the interface are polarized. The results obtained are compared to recent spin- and angleresolved photoelectron spectroscopy experiments. Good agreement with experiment is obtained in the case of a fcc Rh configuration. INTRODUCTION Kachel et al. Il] have recently shown through spin-resolved valence-band and core level spectroscopy that very thin films of Rh coated on Fe(001) are ferromagnetically ordered at room temperature. Through ab-initio calculations using the full-potential linear augmented-plane wave (FLAPW) method [I] they found that a perfect Rh monolayer is polarized ferromagnetically with Fe with a magnetic moment of 0.82 ltB. Nothing is said however, in this calculation, about the spin-polarization of a small number of Rh layers grown on Fe. Therefore it is difficult to say 'a-priori', as suggested in the paper by Kachel et al.[l , that the Rh overlayers are ferromagnetically ordered at room temperature. In fact, as discussed recently by different authors, Rh may present some antiferromagnetic (AF) polarization near the (001) surface [2], in thick Rh films (3 to 6 layers) [3] or as Rh clusters adsorbed on Ag(001) [4]. The origin of this AF-like coupling is unclear. Heine and Samson [5] have discussed the type of magnetism which may appear in the transition-metal series and proved that AF coupling is favored in the middle of the series whereas ferromagnetic (F) coupling can be present at the beginning and the end. However only 3D systems were studied in their work. For thin films, the geometry of the problem has a great influence on the spin-polarization. There are in fact two possible reasons for the onset of magnetism in Rh films coated on Fe(001). The first reason is a purely d-d hybridization where the d-band splitting of Fe induces a polarization in the d-bands of Rh. This is usually a short-range effect and has been observed in the case of Pdn/Fe(001) [6] : the Pd atoms in the film are found to be polarized in contrast with Pd atoms and Pd bulk crystals where no magnetic moments are present. The second reason is related to the so-called coordination effect which relates the magnetic moment of a given atom to the number of its nearest-neighbor (n.n.) atoms: the lower the number of n.n. atoms, the higher the magnetic moment. For example, a perfect monolayer of Rh on Ag(001) has been found to be ferromagnetic
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