Exchange bias is a magnetic interface phenomenon in thin film heterostructures originating from the interaction of magnetic layers in atomic proximity. Quantum mechanical exchange couples antiferromagnetic or magnetically hard substrates with adjacent ferromagnetic thin films. Most strikingly, the coupling shifts the coercive fields of the hysteresis of the top ferromagnet. This phenomenon impacts the technology of magnetic read heads, recording media, and spintronic applications. In collaboration with Hitachi Global Storage Technologies ferromagnetic bilayers are studied where field-induced tailoring of the exchange bias is achieved [Phys. Rev. Lett. 96, 067201 (2006)]. Here, set fields imprint spin states which evolve when consecutively cycled hysteresis loops are measured. Understanding this aging or training effect impacts potential applications based on exchange bias. Its ultimate control is envisioned by electrical means (see Fig.) where magnetoelectric films such as Cr2O3 give rise to electrically induced interface magnetization. The latter provides electrically controlled exchange bias of the ferromagnetic top layer.
This research is supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0213808.
