S. Bouarab

The Pd polarization at the Pd/Fe interface

Abstract The electronic and magnetic properties of the ground state ( T =0 K) at the Pd/Fe(001) interface were investigated through the mean-field parameterized tight-binding method. Structurally, the Pd overlayers occupy the fcc sites of the substrate, with a few percent expansion of the Pd-Pd distances as compared to the bulk fcc Pd. We report results concerning deposition of n Pd layers on semi-infinite Fe. Ferromagnetic polarization of the Pd n layers are obtained up to n =3. For n =4, we have obtained ferromagnetic polarization of the nearest neighbour Pd overlayer but negative polarization for the three other planes. For n =5, all the Pd atoms are polarized ferromagnetically unless the surface which has a quasi-zero magnetic moment. In the case of sandwiches Fe m /Pd n /Fe m or superlattices (Fe m Pd n ) p we investigate both ferromagnetic and antiferromagnetic couplings between Fe films through the Pd spacer. For completeness we perform also total energy calculations in order to study the exchange coupling displayed by Celinski and Heinrich [J. Magn. Magn. Mater. 99 (1991) L25]. Similar trends are found: ferromagnetic coupling is shown to be stable until n =5 for Fe 5 /Pd n /Fe 5 sandwiches; antiferromagnetic coupling is however stable for n =6. We discuss the importance of the interface roughness on this oscillation.

Onset of magnetism in transition-metal monolayers: V and Rh on Ag(001)

Abstract We discuss the onset of magnetic structures in very thin V and Rh overlayer slabs on an Ag(001) substrate in terms of the exchange integral J . We use a self-consistent real-space tight-binding method in the unrestricted Hartree-Fock approximation to the Hubbard Hamiltonian. In both cases, the results display onset of magnetism essentially in the monolayer range. For thicker coverage of Ag(001), the magnetism is quickly killed. This thickness dependence of the magnetism may explain discrepancies between the experimental results performed with various techniques in different groups, in the case of V on Ag(001). Our simple model for Rh on Ag(001) is not able to reproduce the experimental situation plagued by interdiffusion.

Effect of the crystallographic face on the polarization at the Cr/V interface

Abstract Cr slabs with three layers are shown to present very different types of magnetization depending on the crystallographic face considered. (001) and (111) crystallographic faces show enhanced magnetic moment in the layered antiferromagnetic configuration. (011) however displays smaller enhanced magnetic moment and in-plane antiferromagnetism. The addition of V severely reduces the magnetic moment of the Cr films. Investigation of Cr 3 V 1 (001), Cr 3 V 1 (011) and Cr 3 V 1 (111) slabs display layered antiferromagnetic coupling for (001) and (111), whereas in-plane antiferromagnetism is present for (011). The strong influence of the thickness of the V adlayers is shown.

Magnetism of Rh islands and ordered Rh0.5Ag0.5 alloy on Ag(001)

Abstract Theoretical calculations show a high magnetic moment for Rh overlayer on Ag(001) which is reduced when it is coated by an Ag layer. Surface magneto-optic Kerr effect (SMOKE) and spin and angle-resolved photoemission did not detect any spin polarization for epitaxial Rh monolayers on Ag(001) and Au(001). The influence of the real structure of the overlayer on the magnetic properties of rhodium on Ag(001) is discussed.

Spin polarization in V(001) slabs

Abstract We discuss the onset of layered antiferromagnetic structure in very thin V(001) slabs in terms of the exchange integral J . We use a self-consistent real-space tight-binding method in the unrestricted Hartree-Fock approximation to the Hubbard Hamiltonian. Antiferromagnetic structures occur more readily, i.e. at smaller J values, than ferromagnetic structures. When both paramagnetic and antiferromagnetic solutions are present (for a J value greater than a critical value J c ), the layered antiferromagnetic solutions are always stable. The bilayer is found to be antiferromagnetically polarized; for three layer slabs two types of antiferromagnetic solution are obtained. Our results display the variety of possible magnetic behavior in metallic films and give some insight into the controversial situation on V(001) surface.

Thickness dependence of the spin polarization in V(001) and Pd(001) slabs

Abstract We report the electronic structure of free-standing V(001) slabs and of Pd layers grown on Ag(001) through self-consistent real space description of the Hubbard Hamiltonian. The layered antiferromagnetic structure of V(001) slabs with different thicknesses does not display a great difference. The ferromagnetic structure of an n layers slab of Pd grown on Ag(001) displays ferromagnetism for an intermediate value of n whereas paramagnetism is present for n = 1 and n ⪢ 3.

On the magnetic order of ultrathin Mn layers on Fe(001)

Abstract Using an intra-atomic exchange integral J Mn as a fitting parameter in a self-consistent tight-binding model calculation with 3d-orbitals only, we have studied the magnetic behaviour of ultrathin Mn films on Fe(001) for parallel (P) and antiparallel (AP) coupling at the Fe/Mn interface. For a single Mn monolayer on Fe(001) we find a sensitive dependence of the magnetic moment on J Mn . In the AP case, there is a rather sharp, but continuous transition from a low-spin state with μ Mn ≈ 0.4 μ B for J Mn J c to a high-spin state with μ Mn ≈ 4μ B for J Mn > J c . The experimental value of ∼ 2.9μ B lies in the transition region of the energetically favoured P coupling which exists only in the high-spin state.

Electronic, magnetic, and optical properties of

The self-consistent ab initio energy bands of are calculated by the linear-muffin-tin-orbitals (LMTO) method with local spin-density approximation (LSDA). For the non-magnetic phase, we have used cubic perovskite structure with one formula unit, whereas, for the magnetic phase, A-, C-, or G-type tetragonal or orthorhombic structures with higher numbers of formula units are considered. The non-magnetic energy bands predict the right tendencies as regards the existence of magnetism in the series. The calculated magnetic moments and magnetic phases are compared with those found by experimental measurements. These energy bands are further used to calculate the optical conductivity in the visible and ultraviolet regions. Only a few samples of have undergone optical conductivity measurements, with which our results are in comparatively good agreement. With the rest of the compounds, our theoretical calculations can be seen as precursors for future experiments.

Competition between CoCr hybridization and low-coordination effects in the magnetism of a Co monolayer deposited on Cr substrates

Abstract We present a tight-binding study of the magnetism (local magnetic moments, magnetic order and average magnetization) of a Co monolayer grown on Cr(001) and Cr(107) substrates. It is found that the Co Cr hybridization strongly reduce the spin polarization of the Co overlayer in agreement with recent experimental observations. At the same time, the presence of local steps at the surface, ocurring for instance at the (107) substrate of Cr, leads to an increase of the spin polarization of the less coordinated Co atoms. The competition between both effects is discussed for the two different magnetic configurations Obtained as solutions of our self-consistent tight-binding model. The results are compared with experiments where magnetically dead Co layers are found when deposited on Cr(001).

Effect of V on the short oscillatory period in Fe/Cr superlattices

Abstract A self-consistent tight-binding calculation with 3-d bands only is used to derive the local magnetic polarization at the interfaces between Fe, V and Cr and the interlayer magnetic couplings in Fe3VnCrm. The two-layer period oscillation of the exchange coupling obtained in the case of a Fe/Cr/Fe(001) wedge structure is destroyed for n = 1, 2, whereas it remains in the case of n = 3.