Small and large angle precession in exchange biased bilayers

Both small and large angle precession of a ferromagnetic layer upon photoexcitation can be modeled with reasonable values of the Gilbert parameter within the Landau-Lifshitz and Gilbert framework. Employing the known antiferromagnetic thickness dependence of the exchange bias field, the exchange bias field dependence of the Gilbert parameter is investigated. For this purpose, a wedge shaped exchange bias bilayer with a fixed thickness of the ferromagnetic layer and a varying thickness of the antiferromagnetic layer along the sample is prepared and measured. The extracted Gilbert parameter from the time-resolved Kerr traces, hence the dissipation rate, increases linearly with the exchange bias field magnitude. Local fluctuations of the interfacial coupling due to interface roughness can increase the two-magnon relaxation probability, which in terms of an additional dissipation channel finally leads to an increased Gilbert damping parameter.