Exchange bias (EB), the interfacial coupling between a ferromagnet (FM) and an antiferromagnet (AFM) has been a widely studied phenomenon since its discovery. It has been studied in bilayers, core-shell clusters, and nano-structured materials. However, the use of ion implantation and irradiation has been limited so far to the modification of pre-existing exchange bias systems. In this work we present the successful application of ion implantation to generate an EB system [1], rather than to modify it. We implanted O ions in thin Co films (100 nm) in order to form CoO, embedded in the film. The coupling between the formed CoO and the Co matrix gives rise to EB. We show the feasibility of this approach and prove that the observed EB is a consequence of the formation of CoO and not of implantation related damage, by comparison to Ne implanted Co films. Furthermore, this system exhibits a clear training effect, i.e. the EB effect depends on the number of times the hysteresis loop is measured. In the more conventional EB bilayers, this effect is understood by a change in magnetization reversal mechanism. Due to the clear morphological differences of the FM-AFM interface between this implanted system and bilayers, a strong influence on the reversal mechanism is anticipated. Therefore it was studied with anisotropic magnetoresistance and polarized neutron reflectometry. Both measurements reveal a radically different behavior from bilayers: all reversals are governed by domain wall nucleation and motion, where in bilayers a change from domain wall nucleation and motion to coherent rotation is observed.

[1] J. Demeter, J. Meersschaut, F. Almeida, S. Brems, C. Van Haesendonck, A. Teichert, R. Steitz, K. Temst, and A. Vantomme, Appl. Phys. Lett. 96 (2010) 132503

Joost Demeter, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium
Johan Meersschaut, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium
Francisco Almeida, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium
Steven Brems, Laboratorium voor Vaste-Stoffysica en Magnetisme, K.U.Leuven, Belgium
Chris Van Haesendonck, Laboratorium voor Vaste-Stoffysica en Magnetisme, K.U.Leuven, Belgium
Anke Teichert, Helmholtz Zentrum Berlin für Materialien und Energie, Berlin, Germany
Roland Steitz, Helmholtz Zentrum Berlin für Materialien und Energie, Berlin, Germany
Kristiaan Temst, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium
André Vantomme*, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium

*presenting author