Influence of the electrical resistivity of a ferromagnetic thin film on its permeability measurement performed with a permeameter

Complex permeability mu (= mu' -j(.)mu'') of a Permalloy Ni80Fe20 thin film, deposited on a 0.5 mm thick glass substrate, is investigated in the frequency range from 0.15 to 6GHz using a single-coil method. The results reveal that the frequency-dependent permeability is affected by the way to determine the RLC parameters, describing the cell, which allow extending this broad band technique up to 6 GHz. We show that the interaction between the electric field E, of the TEM mode propagated by the coil, and the electrical resistivity of the ferromagnetic layer can be taken into account experimentally. In this case, the RLC parameters are determined from a preliminary impedance measurement of the cell loaded with the ferromagnetic thin film along its easy axis. Our results are compared with a theoretical spectral permeability assuming a gyroresonance mechanism and an in-plane uniaxial anisotropy in the Permalloy thin film. A very good agreement is obtained with the experimental results and leads to the determination of a constant K that describes the permeameter. Then, permeability measurements are first performed on a ferrimagnetic composite made of Ni0.5Zn0.5Fe2O4 spinel ferrite embedding in a non-magnetic matrix. For a 650 mum thick sample, we point out that the single-coil method is well adapted to measure the high-frequency permeability up to 6 GHz of ferrite composite materials without involving long computations and precise clearances for the samples. (C) 2004 Elsevier B.V. All rights reserved.