Domain wall resonance linewidth of parallel stripe domains: Effect of the relaxational dynamics of the magnetization modulus

Domain wall resonance (DWR) linewidth of parallel stripe domains has been investigated both theoretically and experimentally. From theoretical point of view, the expression of the dynamic susceptibility for rigid and flexural DW's has been generalized by taking into account the relaxational dynamics of the magnetization modulus on the basis of the phenomenological equation of motion proposed by Bar'yakhtar. Experimentally, DWR measurements have been performed on rare-earth bismuth-substituted single-crystal garnet films with a variation of the Gilbert damping parameter alpha(FMR) (2.6X10(-3)less than or equal to alpha(FMR)less than or equal to 3.5X10(-2)). Well-defined DWR lines have been detected for all the samples allowing us an accurate determination of resonance linewidths. From the analysis of the dependence of the DWR linewidth with alpha(FMR), it is shown that the relaxational dynamics of the magnetization modulus contributes significantly to the DWR linewidth for low-damped garnet films (alpha(FMR)<10(-2)) but cannot account wholly for the observed experimental DWR Linewidths. For higher damping parameters, while the effect of the relaxation of the magnetization modulus becomes negligible, the experimental DWR linewidth remains in excess of the theoretical one (about 2.5 times larger for alpha(FMR)=3.5X10(-2)). Introduction of additional losses in the DW oscillations of a parallel stripe domain system (interaction of the DW motion with anisotropy fluctuations, interaction of flexural wall waves) is suggested.