FMR linewidth and the crystallization processes in Co-based amorphous microwires

Abstract

The ferromagnetic resonance (FMR) technique has been used for many years as a tool to characterize the dynamic magnetic properties of bulk, thin film magnetic materials and microwires. Also, the FMR linewidth is associated to the dissipative processes involved on the magnetization dynamics. Such dissipative channels may be separated in two groups: intrinsic and extrinsic ones. While the first one is related mainly to the Landau–Lifshitz (LL) and eddy-currents damping mechanisms, the second one take in to account contributions coming from the inhomogeneities in the sample. Each one of these relaxation processes contributes to the FMR linewidth in a different frequency and/or magnetic field range and they can be separated by an appropriate FMR linewidth measurement. This work presents FMR measurements, obtained by the impedance method, ranging from 100KHz to 1.8GHz, in Joule annealed Co-based amorphous microwires. It is shown that the crystallization process can be followed by the evaluation of the extrinsic magnetization damping terms, specifically analyzing contributions from inhomogeneities to the FMR linewidth. From the fitting of models which consider LL damping term, anisotropy dispersion and magnon scattering to the experimental data, three ranges of annealing temperatures can be distinguished in terms of spin dynamics on the studied samples: annealing temperatures lower than the Curie temperature, a temperature range between the Curie and the crystallization temperature and another temperature range above the crystallization temperature.