Acoustic-domain resonance mode in magnetic closure-domain structures: A probe for domain-shape characteristics and domain-wall transformations

Abstract

The magnetic-domain resonance was studied for varying closure-domain structures in ${\mathrm{Co}}_{40}$${\mathrm{Fe}}_{40}$${\mathrm{B}}_{20}$ thin-film elements. A domain-shape anisotropy model was introduced, by which a significant increase of the acoustic-domain resonance frequency for decreasing domain width is predicted. We show that magnetic flux closure further increases the domain-width effect on the acoustic-domain resonance frequency. Furthermore, the domain resonance frequency is very sensitive to the effective width of the magnetic-domain walls due to dynamic dipolar interaction. The latter is quantified by calculating the dynamic wall width dependent dipolar fields. Domain-wall transitions in external magnetic fields manifest in either smooth or sudden resonance frequency changes, depending on the involved domain-wall types. Quantitative agreement between experimental and modeled data is obtained. Measuring the acoustic-domain resonance in small excitation fields therefore displays a method to analyze domain-wall instabilities and domain-wall interactions.