Robust Oxides for Biasing Read-Heads
  The ever-increasing density of the information stored on computer discs has required the introduction of read-heads which consist of very thin magnetic films which exhibit a change in resistance when a small magnetic field is applied. For optimum performance, these films must be biased such that their magnetization is in a specific direction. The preferred biasing technique is to couple the ferromagnetic read-head film to an antiferromagnetic film, utilizing a phenomenon known as Exchange Anisotropy. The UCSD-MRSEC has pioneered the development and use of stable antiferromagnetic oxide biasing films in preference to metallic films which suffer from corrosion. The phenomenon of Exchange Anisotropy has been recognized for more than 40 years, but an understanding of its origin has only recently been developed by researchers at the UCSD-MRSEC.

Antiferromagnetic materials do not have a net magnetization since, by definition, they have equal numbers of magnetic spins in opposite directions. However, at the surfaces of polycrystalline antiferromagnetic films, the existence of interfacial roughness, grain size distributions, grain boundary disorder, and different crystallographic orientations, produces uncompensated spins - i.e., spins with no antiparallel neighbor. We have shown that the strength of the biasing produced by Exchange Anisotropy is determined by the density of these uncompensated spins. With this new understanding, we are now investigating methods for increasing the density of uncompensated spins in order to develop even more effective antiferromagnetic oxide biasing films

"Interfacial Uncompensated Antiferromagnetic Spins: Role in Unidirectional Anisotropy in Polycrystalline Ni81Fe19/CoO Bilayers", Kentaro Takano, R. H. Kodama, A. E. Berkowitz, W. Cao, and G. Thomas, Physical Review Letters, 79, 1130 (1997).