Projeto e implementação de uma guia de onda coplanar (CPW) para técnica de FMR via VNA

Abstract

In this work, a study of ferromagnetic resonance (FMR) in Ni81Fe19 (Permalloy) thin films with a thickness of 100 nm was performed. FMR measurements were obtained using the FMR technique via Vector Network Analyzer (VNA), in which the VNA is used in con junction with a coplanar waveguide. The VNA-FMR technique allows measurements over a wide frequency band and detects the FMR condition through microwave S parameter measure ments. The coplanar-type waveguide was designed with its dimensions for impedance matching of approximately 50 Ω, simulated for initial evaluation, and subsequently produced using the ProtoMat S103. This waveguide was proposed to make the FMR measurement process more practical and easier compared to measurements made using a stripline waveguide. The real and imaginary components of the S21 parameter of the guide, loaded with the sample, were mea sured at frequencies between 1 - 8.0 GHz with the external magnetic field applied parallel to the plane of the sample along the direction of propagation of the electromagnetic waves. Resonance frequencies and half-height line widths were obtained by fitting the ReS21 vs. H using an equa tion composed of a synmetric term (Lorentzian curve) and an anti-symmetric term (dispersive curve). The dependence of the resonance frequency on the applied external field was fitted with Kittel’s relation. The Gilbert damping coefficient was obtained from the ∆H vs. f. The results obtained show that, besides obtaining satisfactory values for FMR measurements it is evident through the presentation of the whole methodology of idealization of the waveguide involved its usefulness in FMR experiments.