Magnetism and Magnetic Interactions at Transition Metal Surfaces and Interfaces
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Magnetism and Magnetic Interactions at Transition Metal Surfaces and Interfaces 2
Ruqian Wul, Dingsheng Wang" and A.J. Freeman' 1 Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208-3112 2 Institute of Physics, Academia Sinica, Beijing 100080, P.R. China
ABSTRACT In the exciting field of low dimensional magnetic systems including surfaces, interfaces and thin-films, local spin density (LSD) functional ab initio electronic structure calculations have played a key role by not only providing a clearer understanding of the experimental observations but also predicting new systems with desired properties. Our extensive calculated results demonstrate that: (i) magnetic clean surfaces or interfaces with inert substrates undergo strong magnetic moment enhancements; (ii) the strong interaction with nonmagnetic transition metals diminishes (completely in some cases) the ferromagnetism and usually stabilizes the antiferromagnetic configuration. By including spin-orbit coupling as a perturbation, (i) reliable results for the magneto-crystalline anisotropy of ultra-thin films can be obtained using the state-tracking procedure, although the anisotropy energy is a few tenths of a meV; (ii) spectra of the magneto-optical Kerr effects and magnetic circular dichroism in the soft x-ray region can be determined.
INTRODUCTION During the course of the last decade, low-dimensional magnetism of surfaces, interfaces and thin-films has matured into a major branch of modern condensed matter physics and is likely to open vast vistas for practical applications. [1, 2] The abrupt termination of the lattice or composition in these systems leads to a variety of exotic phenomena such as localized electronic states, magnetic moment enhancement, perpendicular magneto-crystalline anisotropy (MCA), complex magnetic ordering, etc. Fortunately today, it is possible to synthesize and study thin films with either stable or metastable phases, and this has dramatically and importantly increased the range of materials that are magnetic and hence the challenges for understanding magnetism in low dimensional systems. It is known that ab initio numerical energy band methods (mainly the full-potential linearized augmented plane wave (FLAPW) method) based on local spin density (LSD) functional theory have played a very important role in the development of lower-dimensional magnetism. [3] Theoretical calculations predicted the large enhancement of the magnetic moment for 3d transition metal (TM) surfaces or TM ultrathin films deposited on inert substrates, [4] and possible magnetism in some normally non-magnetic materials [5]; some of these predictions have been already verified experimentally. [6, 7]. Stable magnetic structures, especially some antiferromagnetic (AFM) configurations, can now be predicted by comparing total energies and, in the same way, equilibrium atomic geometries and lattice relaxation (including surface and interface) can also be determined. Very recently, we proposed and implemented a state-tracking procedure to
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