Unusual Phenomena in Exchange-Biased Nanostructures

Abstract

The following article is an edited transcript based on the MRS Medalist presentation given by Ivan K. Schuller of the University of California, San Diego, on December 3, 2003, at the Materials Research Society Fall Meeting in Boston. Schuller received the MRS Medal for “his innovative studies of exchange bias in magnetic heterostructures and nanostructures.” Magnetic nanostructures have received increasing attention in recent years, motivated by the interesting phenomena that are apparent when physical size becomes comparable with relevant magnetic length scales. In addition, a number of important potential applications in the sensors and storage industries have emerged. When magnetic nanostructures are in contact with dissimilar magnetic materials, and because their magnetic fields extend considerably outside the physical structure, they are very susceptible to interaction with the surrounding environment. A particularly interesting situation is a ferromagnetic nanostructure in contact with an antiferromagnetic substrate. In this “exchange-biased” configuration, a variety of unusual phenomena arise: The reversal mode of the ferromagnet changes considerably, the superparamagnetic transition temperature is affected, and there is a noticeable change in the microscopic spin configuration. A series of experiments will be described involving these phenomena in nanostructured ferromagnets prepared by electron-beam lithography and self-assembly