Anomalous spin-wave damping in exchange-biased films

Ferromagnetic resonance and Brillouin light-scattering techniques have been used to investigate the spin-wave damping in ferromagnetic (FM)/antiferromagnetic bilayers exhibiting exchange bias. The measurements were done in the prototype system NiFe/NiO sputtered on Si(100) as a function of the NiFe film thickness. The linewidths measured with both techniques are more than one order of magnitude larger than in similar NiFe films without exchange bias and increase dramatically with decreasing FM film thickness. The data are consistently explained by a relaxation mechanism based on two-magnon scattering processes due to the local fluctuation of the exchange coupling caused by interface roughness. The local interface energy necessary to account for the measured linewidths is on the same order of the atomic exchange coupling.