Magnetism on a Microscopic Scale
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tron exchange, and the exchange lengths in most magnetic materials are only a few atomic spacings. Hence, progress depends crucially on the preparation of samples with atomic-scale control of growth, on the performance of clean experiments, on the proper characterization of the physical, chemical, and magnetization structures, and on the constant interaction of experiments with theory. In this issue, some of the leading researchers in the field of magnetism discuss not only current issues, both from a fundamental and a technological point of view, but also newly emerging techniques that help researchers probe these phenomena on a microscopic scale. The articles address these issues in three broad categories defined by length scales, dimensions, and morphologies: (1) surfaces and ultrathin films, (2) multilayers, and (3) thin films.
Ferromagnetism in Reduced Dimensions: Surfaces and Ultrathin Films The 3d transition-metal series contains some of the most commonly used and interesting magnetic materials, for example, Cr, Mn, Fe, Co, and Ni. In their elemental form, they exhibit either ferromagnetic or antiferromagnetic structures. However, when they are grown as ultrathin films, their surface magnetic arrangements are sensitive to the local atomic environment, surface defects, epitaxy/nature of the substrate, and the orientation/perfection of the interface. Surface magneto-optic Kerr effect (SMOKE) has emerged as a versatile probe capable of obtaining surfacemagnetization hysteresis loops with monolayer sensitivity in situ in vacuum. Qiu and Bader discuss this important technique with an excellent choice of examples from surface magnetism and also illustrate its application in studies of surface-magnetic phase transitions. In addition to such surface-magnetization measurements, significant progress in
the field has been made possible by the ability to obtain details of surface structure (crystallography and morphology) dynamically during growth and to correlate changes in growth parameters on the surface-magnetic domain structures. Spin-polarized, low-energy electron microscopy (SPLEEM) is a global-imaging technique that features the parallel imaging of the reflected intensities obtained by illuminating the sample with polarized electrons. The asymmetry in reflected intensity for incident electrons of opposite polarization is sensitive to surface-magnetic contrast. Even though SPLEEM is a relatively new technique (presently only three instruments are operational worldwide), the article by the pioneers involved in its development (Poppa, Bauer, and Pinkvos) conveys some exciting prospects for its use. Combined with the atomic step vertical resolution in imaging [low-energy electron microscopy (LEEM)] and structural information via diffraction [low-energy electron diffraction (LEED)], SPLEEM offers the capability for true in situ studies of dynamic surface-magnetic processes.
Magnetic Multilayers: Interlayer Coupling and Galvanomagnetic Properties Successive ferromagnetic layers of nanometer-scale thicknesses, s
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