Magnetism on the Nanometer Scale: Disordered Crystalline and Amorphous Magnets, Magnetism in Thin Layers, at Surfaces and Interfaces.

Magnetism is one of the areas of materials science were the design of man-made new materials for specific applications is becoming current practice. Examples are soft amorphous magnets for the use in transformer cores and as magnetic sensors, the new hard magnetic materials based on nitrogenated intermetallic compounds, ultrathin magnetic multilayers with a vast potential in magnetic recording applications, and nanocrystalline permanent magnetic materials. For many of these materials it turns out that the characterization of the materials properties on a microscopy scale by laboratory experiments is difficult, and often insufficient. Hence it is important to fill these gaps by computer experiments. In our group we have developed new computational tools that are very well suited for this purpose: * A real-space tight-binding linear-muffing-tin-orbital (RS-TB-LMTO) technique based on either local-spin- density- or Hubbard-Stoner exchange Hamiltonians and allowing for different orientations of the local spin- quantization axes on the atomic sites. * A tight-binding Greens-function technique for the calculation of the bilinear and biquadratic exchange-pair interactions in bulk magnetic surfaces and thin films. This bridges the gap between the band-theory of itinerant magnetism and classical spin-Hamiltonians that serve as the basis for computer simulations of magnetic phase transitions. * A spin-polarized version of the Vienna ab-initio simulation program VASP based on a plane-wave basis and optimized ultrasoft pseudopotentials, allowing for an ab-initio molecular-dynamics. These techniques have been applied to a wide range of problems of fundamental interest for the physics of magnetic materials and for their prospective technological applications: * Noncollinear magnetism in disordered materials: amorphous magnets, spin-glasses, disordered permanent- magnet materials, giant magneto-resistance compounds. * Magnetic structure and magnetocrystalline anisotropy in crystals, at crystals, at crystalline surfaces and in thin magnetic films. * Surface- and interface phase transitions in thin magnetic films. * Magnetism in quasicrystalline alloys. We propose a project continuing this line of research, concentrating on: * The further development of the computational tools, with the aim of investigating the coupling between the structural and magnetic degrees of freedom and of an improved treatment of spin-orbit contributions to the magnetic anisotropy. * The magnetic structure and anisotropy in thin magnetic films on nonmagnetic substrates and in multilayers with nonmagnetic or antiferromagnetic spacers, with particular attention to the influence of a possible reconstruction of the surface or interface and of the morphology of the films or layers (roughness of surface or interface, formation of surface or interface alloys). * The magnetic properties of antiferromagnetic overlayers on ferromagnetic substrates (or vice versa) and of ferro/antiferromagnetic multilayers, the investigations will concentrate on the effect of the frustration of the magnetic exchange interactions across the ferromagnetic/antiferromagnetic interface and consider the possibilities of the formation of noncollinear spinstructures, of magnetically induced reconstructions and of surface/interface alloying. * The magnetic properties of partially disordered permanent magnet materials and hard magnets * The properties of exchange-coupled hard and soft magnets. * The magnetic structure of intermetallic compounds showing giant or colossal magnetoresistance. The traditionally intense collaboration with theorists in Czechia (Brno, Prague) and Slovakia (Bratislava, Kosice) will be continued during this project. A close cooperation on thin-film magnetism has been started with the Institut de Physique et Chimie des Matèraux de Strasbourg.