Unusual Phenomena in Exchange-Biased Nanostructures

The following article is an edited transcript based on the MRS Medalist presentationgiven 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 theMRS Medal for "his innovative studies of exchange bias in magnetic heterostructuresand nanostructures. Magnetic nanostructures have received increasing attention inrecent years, motivated by the interesting phenomena that are apparent when physicalsize becomes comparable with relevant magnetic length scales. In addition, a number ofimportant potential applications in the sensors and storage industries have emerged.When magnetic nanostructures are in contact with dissimilar magnetic materials, andbecause their magnetic fields extend considerably outside the physical structure, theyare very susceptible to interaction with the surrounding environment. A particularlyinteresting situation is a ferromagnetic nanostructure in contact with an antiferromagneticsubstrate. In this "exchange-biased" configuration, a variety of unusualphenomena arise: The reversal mode of the ferromagnet changes considerably, thesuperparamagnetic transition temperature is affected, and there is a noticeable changein the microscopic spin configuration. A series of experiments will be described involvingthese phenomena in nanostructured ferromagnets prepared by electron-beamlithography and self-assembly.