Ferromagnetic Resonance Properties of NbCrFeCrNb multilayer stacks*

It is by now well established that the presence of a spatially varying magnetization at a SC/FM interface can generate long range spin-polarized triplet supercurrents into the FM via the proximity effect in combination with spin mixing and spin rotation processes. Indeed junctions made up of Nb/Cr/Fe/Cr/Nb layers have been shown to carry supercurrents through significant thicknesses of Fe, showing that this combination of layers supports the generation of long range spin triplet superconductivity [1]. Quite separately, it has been recently demonstrated that spin pumping by ferromagnetic resonance (FMR) of Py when embedded in a Pt/Nb/Py/Nb/Pt stack also supports the formation of long range triplet superconductivity [2]. The characteristic signature of a spin triplet supercurrent in the latter case was an anomalous broadening of the FMR linewidth below the superconducting critical temperature (T_C). In the current work we report on the FMR properties of Nb/Cr/Fe/Cr/Nb stacks, to study the behaviour of the intrinsic linewidth above and below T_C and to establish characteristics indicative of triplet superconductivity.
[1] J. W. A. Robinson et al., Physical Review B 89, 104505 (2014) [2] K-R Jeon et al., Nature Materials 17 499-503 (2018)