The role of uncompensated spins in exchange biasingI. Schmid1, P. Kappenberger1, O. Hellwig2, M. J. Carey2, E. E. Fullerton2 and H. J. Hug1, 3
1 Empa, Swiss Federal Laboratories for Materials Testing and Research - CH-8600 Dübendorf, Switzerland
2 Hitachi Global Storage Technologies - San Jose, CA 95135, USA
3 Institute of Physics, Universität Basel - CH-4056 Basel, Switzerland
received 7 May 2007; accepted in final form 28 October 2007; published January 2008
published online 19 November 2007
The origin of the exchange bias (EB) effect has been traced back to the existence of pinned uncompensated spins (UCS) in the antiferromagnet (AFM) or at its interface. However, the understanding of the underlying mechanism is still clouded by contradictory reports: For example, both a parallel as well as an antiparallel orientation of the UCS relative to the magnetization direction of the ferromagnet (FM) were reported for similar FM/AFM systems. Here different magnetization histories in magnetometry and magnetic force microscopy measurements are used advantageously to demonstrate the co-existence of pinned UCS that are parallel and antiparallel to the cooling field in metallic (IrMn) and oxidic (CoO) EB systems. We further conclude that the EB effect is mainly a result of pinned interfacial UCS, which are antiparallel to the FM spins.
75.70.-i - Magnetic properties of thin films, surfaces, and interfaces.
75.60.-d - Domain effects, magnetization curves, and hysteresis.
75.25.+z - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.).
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