Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR) have been used for complementary studies of the various excited modes in exchange-coupled $\mathrm{Ni}\mathrm{Fe}\left(30\mathrm{nm}\right)∕\mathrm{Ru}\left(d_{\mathrm{Ru}}\right)∕\mathrm{Ni}\mathrm{Fe}\left(30\mathrm{nm}\right)$ films with variable Ru thicknesses $d_{\mathrm{Ru}}$. For antiferromagnetically coupled layers, two modes, which vary in their relative intensity as a function of the bias field, are detected. These two modes, which are observable simultaneously over a limited range of the bias field with PIMM, are identified as optic and acoustic modes. The mode frequencies and the interlayer exchange coupling are found to oscillate as a function of the Ru layer thickness with a period of $8.5\mathrm{\AA }$. The frequency oscillations of the optic mode are coupling dependent, while those of the acoustic mode are indirectly related to coupling via the canting angle of the layer magnetizations below the saturation. Comparison between PIMM and VNA-FMR in terms of frequency of modes shows good agreement, but the optic mode is observed over a wider field range with VNA-FMR. Furthermore, we clearly observed different behaviors of the FMR linewidths as a function of the spacer thickness for the optic and acoustic modes. In addition, perpendicular standing spin waves have been studied as a function of coupling. The FMR linewidth of the different modes increases with the microwave frequency and typical damping constants of $\alpha =0.0073$ have been measured. The effect of the pulse field amplitudes on the properties of the various excited modes has been simulated and studied experimentally.

• Received 24 February 2007

DOI:https://doi.org/10.1103/PhysRevB.76.104414