Belmeguenai, M. and Martin, T. and Woltersdorf, Georg and Bayreuther, Günther and Baltz, V. and Suszka, A. K. and Hickey, B. J.
Microwave spectroscopy with vector network analyzer for interlayer exchange-coupled symmetrical and asymmetrical NiFe/Ru/NiFe.
Journal of Physics: Condensed Matter 20 (34), p. 5206.
Vector network analyzer ferromagnetic resonance spectroscopy (VNA-FMR) is used here to study the different excited modes of sputtered
asymmetrical NiFe(13.6 nm)/Ru(d(Ru))/NiFe(27.2 nm) exchange-coupled
films with variable Ru thicknesses. The obtained results have been
compared to those of the symmetrical NiFe( 30 nm)/Ru( dRu)/NiFe( 30
nm). In both cases, the measurements show the existence of an optic and
an acoustic precessional mode. The optic mode was only observed over
limited field ranges, especially in the symmetrical trilayers. To
overcome such a limitation, we developed a new technique similar to the
longitudinal FMR, where the bias and the rf field are parallel to each
other and perpendicular to the pinning field. Interestingly, and in
contrast to the symmetrical trilayers, we observed a mode anti-crossing
in the dispersion relation of the asymmetrical layers that we
attributed to the thickness difference between the two NiFe layers. Our
experimental results on the effect of the biquadratic coupling on the
mode frequency variations are in good agreement with the theory.