Permeability resonances in permalloy stripes (abstract)

This work presents the experimental low field (Hac≊0.01 Oe) complex permeability spectra μ(f)=μ’(f)−jμ‘(f) (between 1 and 200 MHz) of L=1‐cm‐long NiFe stripes as a function of stripe width W (10 μm to 1 cm), film thickness T (0.1 to 4 μm), and the history‐dependent initial domain configuration. It will be demonstrated that occurrence of strong resonances in μ(f) is closely linked to the domain structure of the stripes, and in particular the linear density of the 180° transverse domain walls (observed by Bitter techniques) characteristic of a periodic flux‐closed domain pattern. Square films (L=W=1 cm) of all measured thicknesses that have a low linear density (<30 walls/cm) of 180° domain walls show no observable resonances, and their spectra μ(f) are instead well described by classical eddy current predictions. In contrast, highly pronounced resonance peaks (μ‘≳μdc≊2000) are observed in 0.1 μm≤T≤2 μm stripes that have been anhysteretically demagnetized with a longitudinal field, where the static domain s...