During the past decade or two, we have achieved an understanding of matter at the atomic and molecular level sufficient to enable the theorist to predict with remarkable accuracy the properties of compounds not found in nature. Materials preparation methods have also advanced to the point where artificial structures can be made in the laboratory which are virtually perfect on the atomic scale. As an example, one can fabricate materials referred to as superlattice structures. These consist of alternating films of two materials A and B, to form a new material with the films stacked in the sequence . . . .ABABAB. . . . The individual films may be only a small number of atomic layers thick. One can make superlattices out of semiconductors, magnetic films, or other materials with interfaces nearly perfect on the atomic scale. The properties of the resulting structures can differ dramatically from those of any naturally occurring material in nature, and these properties are subject to design in the laboratory, by varying film thicknesses, the materials used, growth conditions and other variables. These are thus truly an example of "designer materials", and belong to a larger class of artificial structures referred to as "nanostructured materials". A nanometer is one billionth of a meter. A typical atom or small molecule has a size of roughly one tenth of a nanometer, so nanostructured materials are those crafted in the laboratory with structures that are only a few atomic diameters in size. In addition to the superlattices, which one may say are made from "nanofilms", one may create "nanowires" and "nanodots".
These small scale structures are not just laboratory curiosities, but are entering the everyday world around us. Current semiconductor chips are currently etched with features on the scale of 300 nanometers, and every year these get a bit smaller. A less well known example is provided by magnetic superlattices, where material A may be a ferromagnet such as Fe, and material B a simple non-magnetic metal; the film thickness are at most a nanometer or two. These structures exhibit a most remarkable property discovered recently (1988) known as "giant magnetoresistance" (GMR). If one applies a magnetic field to a metal, its electrical resistance will change. This is the phenomenon known as magnetoresistance. These changes, while of great interest to those who pursue the fundamental physics of the metallic state, are a few percent at best, and thus are of little practical importance. However, one may design magnetic superlattices where the resistance change produced by even a modest magnetic field is enormous by comparison, perhaps a factor of two. These "designer magnetic materials" can be used as magnetic sensors of extraordinary sensitivity; they operate at room temperature. Very shortly, these will appear in magnetic recording heads made by the primary manufacturer in the field. The magnetic recording industry is a multi-billion dollar annual enterprise, and GMR heads will become the standard in the very near future. In five years, your car may have several GMR based monitors, and many argue these new structures will form the basis for a new generation of high density magnetic data storage devices.
The Department of Physics and Astronomy at UCI has been an active center of research into the fundamental physics of nanoscale magnetic films, and nanoscale magnetic multilayers or superlattices. Prof. Herbert Hopster has a very sophisticated laboratory in which state-of-the-art nanoscale films and structures may be fabricated, and studied by a diverse array of techniques, including the use of spin polarized electron beams in various modes. The present author is active in theoretical studies of issues in the area. The two groups have by now made important and fundamental advances in this new field. I am particularly proud that my former Ph. D. student, Bob Camley, still a collaborator and now a Professor at the University of Colorado, is the originator of the basic theory of giant magnetoresistance in magnetic superlattices.
A most exciting new research program has just been founded, in the form of a collaboration between myself, Prof. Hopster, and two distinguished faculty in the UCI School of Engineering, Prof. C. S. Tsai and Prof. C. C. Li. This is the first collaborative effort between researchers in the School of Physical Sciences, and the School of Engineering in the history of the UCI campus. We have argued that by depositing magnetic "nanofilms" on semiconducting films, one has the possibility of realizing a new generation of high frequency magnetic devices. The notion is that the semiconductor will act as a dielectric waveguide for microwaves or laser light, and these fields penetrate into the magnetic film; its magnetism offers the means to manipulate or modify the electromagnetic signals. This new effort, funded by the Army Research Office, combines Prof. Hopster's expertise in the fabrication of superb ultrathin films, where near perfection is realized on the atomic scale, with Prof. Tsai's background in integrated optics and magneto-optic devices. Prof. Li is an expert on the microfabrication methods required to couple energy into and out of the structures, and a theoretical component will be added by the combined efforts of myself and Prof. Camley. The effort has been underway for nearly a year at the time of this writing, and we are all very excited. It will also offer a most interesting opportunity to graduate students in the two Schools, who can pursue thesis research in a unique collaborative environment.
In the near future, it is very clear that we will see exciting new applications of nanostructured "designer materials" not only in device applications such as those mentioned above, but in biology and medical science. A real revolution is underway, in the view of this writer. The key role played by materials in our life, with emphasis on exciting recent developments made possible by the deep understanding which physicists and chemists have acquired recently, is elucidated in the fascinating book "Stuff", written by Ivan Amato.