Abstract
This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features.
Highlights
Their implications on device applications are still to be understood
We investigate from a modelling point of view the influence of randomly distributed lattice defects on the ferromagnetic resonance (FMR) behaviour and spin wave mode profiles of 2D Ni80Fe20 antidot arrays with hexagonal lattice
We study the combined effects of local variations in the hole size and non-patterned regions. These effects are illustrated by the FFT power spectra reported in Fig. 5a, where the black curve corresponds to the antidot array without defects; the blue one is associated with the disordered array with 10% of filled holes and dh set at 330 nm; the red one refers to a disordered array with 10% of filled holes and containing holes with randomly distributed diameter, ranging from 280 nm to 380 nm
Summary
A micromagnetic numerical approach has been applied to study hysteresis, magnetotransport and FMR properties of Ni80Fe20 antidot arrays with hexagonal lattice, in the presence of microstructural defects (non-patterned areas and variations in hole diameter). The presence of non-patterned regions lead to a modification of the dynamic response of the system with a softening of the edge and localized modes in the FFT power spectra. This is accompanied by a possible amplification of the extended modes at quasi-saturation fields and to a local alteration of spin wave mode profiles. Local variations in the hole diameter can lead to a shift in the resonance frequencies of edge and quasi-uniform modes, impacting on the possible use of antidot arrays in frequency-based sensors for magnetic nanoparticle detection. To avoid alterations of the expected FFT power spectra, more frequent for self-assembling samples, fabrication processes based on EBL techniques can be adopted, enabling to obtain well-defined lattice features, but at the cost of low speed and small covering area
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