Pulsed inductive measurement of ultrafast magnetization dynamics in interlayer exchange coupled NiFe∕Ru∕NiFe films

Abstract

Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR), as well as quasistatic methods such as a magneto-optic Kerr effect magnetometer and a vibrating sample magnetometer, have been used for complementary studies of interlayer exchange coupled Si∕Ta∕NiFe(30nm)∕Ru(t)∕NiFe(30nm)∕Ta films of variable Ru thickness t. The coupling constants were determined from the measured magnetization curves by fitting them to simulated ones. The dynamics measurements revealed two spin wave modes, which could be identified as optical and acoustical ones. The optical mode changes significantly with the coupling, whereas the slight change of the acoustical mode is due to different relative orientations of the layer magnetizations. Numerical simulations helped to identify optical and acoustical modes. The intensity of these two modes changes with the bias field and coupling. Using VNA-FMR the optical mode could be observed up to higher bias fields than with the PIMM at small excitation angles. While varying the pulse field up to 150Oe using the PIMM, the intensity ratio of optical and acoustical modes changed and additional modes occurred.