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Exchange anisotropy in CoO/Co thin films

Although exchange anisotropy was discovered back in 1956 (W. H. Meiklejohn and C. P. Bean, Phys. Rev. 105, 904 ~1956), it is not yet clear how it works in detail. With a weak AC magnetic field technique, we could conclude that the strength of the ferromagnetic-antiferromagnetic interaction is much stronger than previously anticipated. This was due to a failed understanding of antiferromagnetic domain wall propagation encountered by the conventional determination of exchange anisotropy from hysteresis loop displacements.

Measured and fitted ac susceptibility response for the partially capped Co (300 Å) sample according to linear decrase, (1-T/T_crit), T_crit = 255K, of the stiffness K_ud for four different field-cooling directions and one zero-field cooled measurement. Here, (a) is in-phase and (b) quadrature response.

Collaboration with Johan Akerman/Jönsson Kista, KTH, Dan Dahlberg Minnesota

V. Ström et al., "Determination of exchange anisotropy by means of ac susceptometry in Co/CoO bilayers," Journal of Applied Physics, vol. 81, no. 8, s. 5003-5005, 1997