A Systematic Ferromagnetic Resonance Study of Deposition Conditions in NiFe Thin Films for Shielding Applications.

Abstract

Tailoring the electromagnetic properties of synthetic magnetic structures is advantageous for high frequency applications, such as engineering shielding materials in magnetic recording where control of properties such as permeability is essential. Design of suitable components requires the characterisation of materials in the gigahertz frequency range to determine the parameters necessary for simulations. We present a systematic study of the dependence of the ferromagnetic resonance (FMR) and spin wave properties of NixFe100-x alloy thin films with varied Ni composition and deposition conditions using a vector network analyser (VNA) and coplanar waveguide [1][2][3][4]. The quality of the FMR response and the effective permeability in single layer films is particularly affected by the NiFe crystal structure, most notably over the fcc-bcc boundary at x=40, Figure 1. The FMR was also improved by proper choice of seed layer and lowering deposition pressure. Increasing substrate temperature was observed to have an actively detrimental effect on ferromagnetic resonance. The effect on FMR of modulating the composition in NiFe thin films was also studied using repeated bilayer structures with a constant total thickness of the form n[NixFe100-x/NiyFe100-y], where n is the number of bilayers and determines the period of modulation. Compared to single layers, the compositionally modulated structures were generally seen to enhance the FMR signal and increase the frequency of resonance, Figure 2.