Ferromagnetic Resonance of Tuneable Low Magnetostrictive NixFe100-x Superlattice Structures for High Frequency Application

Abstract

Tailoring and control of electromagnetic properties of synthetic magnetic structures is advantageous for high frequency applications, such as shielding materials in magnetic recording, where characterisation in the gigahertz frequency range is necessary to determine parameters for simulations and aid component design. In such applications it is desirable to have a high saturation magnetisation, low coercivity, high permeability and close to zero magnetostriction. Meeting almost all these requirements, NiFe is the material of choice for many high frequency applications.We present a systematic study of the ferromagnetic resonance (FMR) and spin wave properties of NixFe100-x alloy thin superlattice films of the form n[NixFe100-x/NiyFe100-y], where n is the number of bilayers. Films were fabricated by planar magnetron sputtering and the effects of deposition conditions were investigated. Magnetic and material properties were measured using FMR [1], vibrating sample magnetometer and x-ray diffraction, with the aim to determine any relation between microstructure and the static and dynamic magnetic properties.Layer compositions within the bilayers have been chosen with particular interest in fcc/bcc layer combinations such as Ni80Fe20/Ni20Fe80, which may have benefits for some static properties such as high magnetisation and low magnetostriction [2]. Studies on single layers have shown dramatic changes in FMR response across the fcc-bcc boundary near x = 40, figure 1. However, for bilayer films it was found that increasing the thickness of the bcc Ni20Fe80 layer in the structure increased the resonant frequency but did not significantly reduce the FMR signal, figure 2.  Fig. 1: FMR spectra of 100nm NixFe100-x single layer thin films with x varying from 10 to 60. Note that all measurements were performed at an applied field H=253Oe. XRD is inset.  Fig. 2: FMR spectra of Ni80Fe20(60-t nm)/Ni20Fe80(t nm) thin films with t varying from 50 to 10. Note that all measurements were performed at an applied field of 253Oe. XRD is inset.