Abstract
We report the results, from experimental and micromagnetic studies, of the magnetic normal modes in artificial square spin ice systems consisting of ferromagnetic-monodomain islands. Spin-wave properties are measured by Brillouin light scattering. The mode spectra contain several branches whose frequencies are sensitive to the magnitude and in-plane orientation of an applied magnetic field. We also identify soft modes that exhibit different behaviours depending on the direction of the applied magnetic field. The obtained results are well described with micromagnetic simulations of independent magnetic elements arranged along two sublattices.
Highlights
Artificial spin ice (ASI) is a class of magnetic materials created by patterning single domain ferromagnetic islands in such a way as to introduce some degree of frustration through interactions determined geometrical constraints [1]
We have investigated the magnetic properties and normal modes of the square ASI using the alternating gradient force magnetometry (AGFM) and Brillouin light scattering (BLS) techniques
The square ASI geometry allows for comparisons between modes in elements with orthogonal alignment
Summary
Artificial spin ice (ASI) is a class of magnetic materials created by patterning single domain ferromagnetic islands in such a way as to introduce some degree of frustration through interactions determined geometrical constraints [1]. Resonances of spin waves can be studied at long wavelengths using Brillouin light scattering (BLS). This technique has been used to obtain experimental. Most importantly for this work, modes exist which are localised to edges of magnetic elements. Since the elements are in a single-domain state, there is a nonuniform distribution of demagnetising fields in the elements, which is most pronounced near the edges and corners These can lead to some curling of the magnetisation within an exchange length of the edges, and mostly serves to affect the frequency of a mode localised to the edge. Mode softening and ‘bell’ shape in frequency versus field have been observed in coincidence with the magnetization reversal for H applied along the ASI edge.
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