Frequency- and time-domain investigation of the dynamic properties of interlayer-exchange-coupled Ni81Fe19/Ru/Ni81Fe19 thin films

Abstract

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 NiFe(30 nm)/Ru(d(Ru))/NiFe(30 nm)
films with variable Ru thicknesses d(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 A. 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.