Modified Gilbert Damping due to Exchange Bias in NiFe/FeMn Bilayers: Abstract DF-12

An all-optical pump probe technique is used to investigate the magnetization dynamics and the magnetic damping behaviour in the polycrystalline Ni80Fe20/Fe50Mn50 exchange bias system. It is demonstrated that the magnetic damping increases linearly with the exchange bias field magnitude. The results can be understood taking the exchange bias effect as an additional dissipation mechanism into account.
In order to investigate the magnetization dynamics an 8.5 ps laser excitation is used. Within the laser pulse duration the temperature is raised, resulting in a collapse of the exchange bias field. Due to the fast recovery time on the order of 160 ps a magnetization precession is induced and the Gilbert magnetic damping parameter is determined by comparison of the experimental data to macrospin simulations on the basis of the Landau-Lifshitz-Gilbert equation. The exchange bias field dependence is studied employing the antiferromagnetic thickness dependence by preparing a wedge shaped FeMn layer (0 – 10 nm) on top of a 5 nm NiFe layer.