A. Mokrani

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.

Very thin Mn films on fcc Co(001)

Abstract The electronic and magnetic properties of a Mn overlayer on Co(001) are investigated by using a tight-binding Hubbard-type Hamiltonian. Multiple possible magnetic arrangements are investigated for the Mn atoms. A competition between c(2 × 2) in-plane antiferromagnetic ordering and antiferromagnetic coupling between a ferromagnetic Mn monolayer and a Co substrate is obtained. These results are compared to recent element specific X-ray magnetic circular dichroism measurements.

Magnetism of vanadium islands on Ag(001)

Abstract The electronic and magnetic properties of the ground state ( T = 0 K) of vanadium islands on Ag(001) were investigated through a mean-field parameterized tight-binding method. The Ag substrate does not affect much the magnetism of the V atoms which is directly related to the V-V coordination number. Therefore, the outermost V atoms present the highest magnetic moment. Antiferromagnetic like coupling is obtained between most of the V atoms at nearest neighboring positions. However, when a vanadium atom is coupled antiferromagnetically to a part of its nearest neighboorhood and ferromagnetically to the other part, its magnetic moment remains very low.

Stepped Fe(001) surface magnetism

Abstract We investigate the magnetic arrangment of vicinal Fe surfaces by using a self-consistent real space tight-binding Hamiltonian. The presence of steps modifies locally the magnetic properties of the ideal flat surfaces. We point out the influence of the atomic environment and we found that, for Fe, the simple rule which relates a decrease of the local magnetic moment to an increase of the coordination number, is valid. The results are not very sensitive to the step length. Finally, arguments are given to explain the more subtle behavior of the surface atom.

Effect of self-consistency in the magnetism of iron in reduced geometry

Abstract A real space self-consistent tight-binding scheme has been used for the description of an 11-layer slab of iron. The magnetism is described in the unrestricted Hartree-Fock approximation of the Hubbard Hamiltonian for d electrons. Different sets of hopping integrals are used. Contrary to a recent claim, we point out the importance of the electronic self-consistency.

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.

Magnetism of Rh vicinal surfaces

Abstract We investigate in detail the magnetic behavior of the (105) Rh vicinal surface. Fully self-consistent tight binding calculations with the Hubbard Hamiltonian are performed. We study especially the onset of magnetism, versus the exchange integral J. This stepped surface displays an onset of magnetism for similar value of J as that for the (001) surface. Simple and empirical rules allow to understand the magnetic moments distribution. Original magnetic configurations are found: all couplings are ferromagnetic, except between the second and the third planes parallel to the step surface. This vicinal surface is no more favorable than the (001) surface to present live magnetism.

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.

Magnetic configurations of rhodium

Abstract Two configurations are, a priori, favorable for a possible magnetic ground state of rhodium: small clusters and very thin films. In both cases, the reduction of the average coordination number could allow the onset of magnetism. For clusters, experimental works indicate that Rh N clusters with N 60 have a non-zero average magnetic moment. By using a d-band Hubbard Hamiltonian, the size and the geometric dependence of the magnetic properties of Rh clusters is studied. Different structures and atomic relaxations are considered. Significant magnetic moments are found up to N 50. For thin films of rhodium on silver, the Ag/Rh interdiffusion inhibits a long range magnetic order. The only favorable case is to consider a magnetic substrate. For thin Rh layers on Fe(001) only mono- and bi-layers are polarized. For larger thicknesses, only an interfacial polarization remains. Finally, in agreement with other studies, the Rh semi-infinite crystal does not display a local magnetic moment.