. "3. Research Opportunities and Functional Roles of Materials." Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials. Washington, DC: The National Academies Press, 1989.
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Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials
for higher-density storage, requiring new storage media; and the emergence of competitive new technologies, such as magnetooptic storage, that call for entirely new classes of magnetic materials. As never before, magnetic materials are the key to the future of the storage industry.
Scientific opportunities in magnetic materials, exciting in themselves, also dovetail in many cases with the technical demands of magnetic applications. An example is the study of magnetic surfaces and interfaces. Control and study of surfaces on an atomic level have proved to be more challenging for magnetic materials than for semiconducting materials. One reason is that detection of magnetic properties requires the use of so-called spin-sensitive measurement techniques, which add extra complexity to the already very sophisticated surface analytical tools used to study semiconductors and other nonmagnetic materials. However, this technology is now largely in place in many laboratories throughout the world, opening the door to an understanding of magnetic surfaces that was never before possible.
Magnetic surfaces and interfaces can give rise to anisotropies and effective fields that become an ever larger factor in the behavior of the bulk material as its thickness decreases, which will be a major consideration in future storage technologies. A specific example concerns the peculiar internal field, called exchange anisotropy, that arises at interfaces between a ferromagnet and an antiferromagnet, causing the ferromagnet to behave as if it were subject to an external field. Such an effect could potentially find application where it is awkward or costly to apply a field with an external power source. This long-puzzling phenomenon is just beginning to be understood in terms of the randomness of the interfacial magnetic structure. Synthesis of more perfect interfaces would offer a conclusive test of the mechanism.
Control of magnetic surfaces and interfaces is also the basis for synthesis of new artificial magnetic materials—multilayers and superlattices. Early experiments have already shown complex couplings between the different magnetic layers, which could be the basis for new properties not available in bulk materials. There is hope for achieving larger anisotropies, coercivities, galvanomagnetic effects, and magnetooptic effects, and there are tremendous varieties of systems to explore. Interest in this area has grown dramatically in the last few years in research groups throughout the world.
Another example of scientific opportunities comes from progress in the band theory of magnetic materials. Using novel statistical techniques and Monte Carlo calculations, researchers are now calculating the Curie temperature of iron with increasing accuracy. This had been a long-standing problem, and its solution opens the door to theoretical prediction of a variety of other magnetic properties. Many of these fall under a common umbrella, the so-called spin-orbit interaction, which gives rise to anisotropy, galvanomagnetism, and magnetooptic rotations. All of these properties have been poorly understood in the past and are decisive for many applications.
Major advances in magnetic materials have been appearing at an accel-