Influence of tantalum underlayer on magnetization dynamics in Ni₈₁Fe₁₉ films

The effect of tantalum (Ta) underlayer is investigated in Ni₈₁Fe₁₉ thin films for magnetization dynamics. The damping parameters extracted from spin wave measurements increase systematically with increasing Ta thickness, whereas the damping parameters from ferromagnetic resonance measurements are found to be weakly dependent on the Ta thickness. The difference is attributed to propagating properties of spin wave and short spin diffusion length in Ta. The group velocity of spin waves is found to be constant for different Ta thicknesses, and nonreciprocity of spin waves is not affected by the Ta thickness. The experimental observations are supported by micromagnetic simulations.