M. Donath

Magnetism and structure in systems of reduced dimension

An Historical Perspective of Key Issues in the Magnetism and Structure of Systems of Reduced Dimensions G.A. Prinz. Advances in Magnetic Disk Storage Technology Y. Miura. Magnetic Domains in Ultrathin Epitaxial Films Observed by Spin-Polarized Scanning Electron Microscopy R. Allenspach. Magnetic-Sensitive Scanning Probe Microscopy R. Wiesendanger. Stabilization of Metastable Phases by Epitaxy M. Piecuch, et al. SEMPA Studies of Oscillatory Exchange Coupling J. Unguris, et al. Giant Magnetoresistance in Transition Metal Multilayers S.S.P. Parkin, et al. Theory of the Perpendicular Magnetoresistance in Magnetic Multilayers A. Fert, T. Valet. The Influence of Magnetism and Structure on Transport Properties and Interlayer Coupling of Systems in Reduced Dimensions P.M. Levy, et al. What Rare Earths Teach about Thin Film Magnetism C.P. Flynn, F. Tsui. 31 additional articles. Index.

Spin-dependent electronic structure at magnetic surfaces: the low-Miller-index surfaces of nickel

Abstract The understanding, on a microscopic level, of magnetic phenomena at surfaces and interfaces hinges on a detailed knowledge of the spin-dependent electronic structure, particularly close to the Fermi level. Experimentally, the most direct access to the spin-dependent electronic states is given by angle-resolved photoemission and inverse photoemission with spin resolution for the emitted and incident electrons, respectively. This report reviews spin-resolved inverse photoemission results on empty electronic states at the low-Miller-index surfaces of nickel as a prototype of a ferromagnetic 3d transition metal. Examples cover bulk-like electronic states, different kinds of surface states, and adsorbate-induced modifications of the surface electronic structure. The data are discussed along with photoemission results on the occupied states. A variety of results is presented which demonstrate how surface magnetic properties are reflected in the spin-dependent electronic structure.

High-Performance GaAs Polarized Electron Source for Use in Inverse Photoemission Spectroscopy

The design and operating properties of a GaAs polarized electron source are presented. An electron optical system is described that passes more than 80% of the emitted electrons at 10 μA to the target under low‐energy (7–20 eV) parallel beam conditions. Laser excitation can give rise to abnormal energy distributions of the photoemitted electron beam. The existence of longitudinal modes gives a possible explanation for this behavior, which can be avoided using a mode stabilized light source. The overall performance of the polarized electron source is demonstrated by inverse photoemission spectra from Ni(110).

Electronic Surface and Interface States on Metallic Systems

Surface states and surface dynamical phenomena, S.D. Kevan vibrations at surfaces and electronic excitations, M. Head-Gordon electronic structure and reconstruction of the Mo(001) surface, J.-W. Chung surface states and the geometric structure, the phonon dispersion and the chemical reactivity of beryllium surfaces, E.W. Plummer the interaction of adsorbates with surface states, E. Bertel low-dimensional electronic states on metal surfaces - quantum wells and quantum wires, F.J. Himpsel STM observation of surface states on Au(111), P. Avouris the role of surface-, interface-, and adlayer-states for the magnetism in ultrathin adlayers, S. Blugel magnetic surface states, M. Donath spin-polarized photoemission studies of interface and quantum well states in thin films, P.D. Johnson surface covalent-metallic transition in gallium and germanium, E. Tosatti. (Part Contents).

Magnetic order and electronic structure in thin films

The magnetic order in ultrathin films depends critically on a variety of film parameters. Therefore, to understand the magnetic properties of thin films on the basis of the spin-dependent electronic structure is a challenging task for both experimentalists and theoreticians. Experimentally, spin-resolved electron spectroscopies probe directly either the spin-dependent density of states or specific energy states, often at a defined wave vector. In this paper, two surface-sensitive techniques, that provide complementary information about the unoccupied electronic states, are described. Spin-resolved appearance potential spectroscopy gives element-specific access to the spin-dependent local density of states. Spin-resolved inverse photoemission permits detailed investigations of electron states characteristic of the surface and the layers underneath as a function of the wave vector. Both techniques are sensitive also to the film structure. A variety of magnetic film properties is discussed in the light of the electronic structure. The examples described in this paper include Fe films on W(110) and Cu(001) as well as Gd films on W(110).

Spin-resolved inverse photoemission of ferromagnetic surfaces

Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism.

Spin-Polarized Dirac-Cone-Like Surface State with d Character at W(110)

The surface of W(110) exhibits a Dirac-cone-like state with d character within a spin-orbit-induced symmetry gap. As a function of the wave vector parallel to the surface, it shows a nearly massless energy dispersion and a pronounced spin polarization, which is antisymmetric with respect to the Brillouin zone center. In addition, the observed constant energy contours are strongly anisotropic for all energies. This discovery opens new pathways to the study of surface spin-density waves arising from a strong Fermi surface nesting as well as d-electron-based topological properties.

Valley spin polarization by using the extraordinary Rashba effect on silicon

The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.

Exchange splitting of an oxygen 2p-derived band at Ni(110)

Abstract Employing spin-resolved inverse photoemission we have observed an exchange splitting of the unoccupied oxygen-induced band in the chemisorption system (2 × 1)-O/Ni(110). At the centre of the surface Brillouin zone the splitting between the oxygen 2p-derived majority and minority band— referred to the magnetization vector of nickel-was found to be 80±20 meV. This effect is a manifestation of the strong magnetic correlation between the oxygen and nickel bands. The size of the splitting is surprising as earlier experimental work indicated a substantial reduction of the surface magnetization due to chemisorption. For the empty 2π∗-derived band of CO on Ni(110) no such splitting has been observed.

Exceptional behavior of d-like surface resonances on W(110): the one-step model in its density matrix formulation

Spin–orbit-induced spin splitting of surface states has attracted great interest in recent years because of the high potential for technological applications associated with this phenomenon. This Rashba physics is found in a variety of systems ranging from simple metals like Ag or Au to the so-called topological insulators which are of special interest in spintronics. A very special and unique case is found at the W(110) surface. In this metal d-like surface resonances exhibit energy dispersions and spin-polarization structures which are reminiscent of topological surface states. In our theoretical study, we present a complete analysis of the surface electronic structure of W(110) and show that the atypical linear-shaped dispersion behavior is triggered by the amount of charge transfer from the bulk into the first few vacuum layers. Furthermore, we compare our theoretical spectra with experimental photoemission data on W(110) and demonstrate that our state-of-the-art photoemission theory is able to deal with these peculiar surface features in a quantitative way. Our analysis is based on a generalization of the relativistic one-step model of photoemission, recently extended by us to study photoelectron spectroscopy at high photon energies. This theoretical approach was realized in the full spin-density matrix formulation for the photocurrent, which allows for an unrestricted calculation of the spin-polarization vector of the photoelectron. As an additional result we predict very peculiar behavior of these surface features showing up even at soft and hard x-ray energies. This observation is very surprising, unprecedented for ordinary surface features on simple metal surfaces.