Microwave damping in polycrystalline Fe-Ti-N films: Physical mechanisms and correlations with composition and structure

Ferromagnetic resonance (FMR) derivative linewidths were measured from 30.3em0exto0.3em0ex120.3em0exGHz on 500.3em0exnm thick sputtered polycrystalline Fe-Ti-N films with 30.3em0exat.0.2em0ex% titanium and a nitrogen content (xN) from 1.90.3em0exto0.3em0ex12.70.3em0exat.0.2em0ex%. The measurements were made with both stripline and waveguide FMR spectrometers. Linewidths were generally lowest at xN=70.3em0exat.0.2em0ex%, with derivative linewidth (ΔH) values in the 15--250.3em0exOe range and a nominally linear increase with frequency $(f)$. This minimum linewidth composition is connected with the bcc to bct structural transition in the Fe-Ti-N system. Linewidths increased at both larger and smaller xN values and were accompanied by the development of a more rounded frequency profile that is indicative of two-magnon scattering. All of the ΔH vs f data could be fitted successfully with a constant inhomogeneity broadening linewidth of 8--110.3em0exOe, a two-magnon scattering (TMS) linewidth from the random grain-to-grain fluctuations in the effective anisotropy field directions for the polycrystal, and a magnon-electron (m-e) intrinsic relaxation term modeled through Gilbert damping with a single α value of 0.003. The actual fits were done through the convolution of a Gaussian linewidth for the inhomogeneity term and a Lorentzian linewidth for the TMS and m-e terms. The fitted anisotropy field parameters from the TMS analysis ranged between 398 and 8830.3em0exOe, with the minimum also at the bcc to bct structural transition at xN=70.3em0exat.0.2em0ex%.