Spin waves in exchange-biased Fe/FeF2

The unidirectional anisotropy in exchange biased ${\mathrm{F}\mathrm{e}/\mathrm{F}\mathrm{e}\mathrm{F}}_2$ bilayers is measured by Brillouin light scattering (BLS) from spin waves in the Fe layer. This technique, where the ferromagnetic layer is always saturated, allows for a straightforward, accurate determination of the exchange bias field. The value obtained from BLS is 25% larger than the one obtained from conventional magnetometry. Moreover, a large broadening of the spin-wave mode due to the presence of the antiferromagnet is observed. From the field dependence of this broadening we conclude that the mode broadening is unidirectional.