Abstract
In this paper, micromagnetic analysis of an array of long magnetic nanowires (NWs) embedded in a nonmagnetic matrix is performed. It is found that for NWs with diameters on the order of a hundred nanometers, the anisotropy and exchange energies are negligible, so the total free energy is a sum of the Zeeman and magnetostatic energies. The minimum magnetostatic energy corresponds to the maximum Zeeman energy, whereby half of the NWs are magnetized parallel to the external field, while the rest of the NWs are magnetized antiparallel to the external fields. The study shows a vortex behavior of the magnetic moments in the magnetization reversal process. Additionally, the hysteresis loop area of the nanocomposite is inversely proportional to the NW diameter in the range from 20 to 200 nm. The results pave the way for designing of NW-based devices such as optimized magnetic sensors for biomedical applications with a trade-off between miniaturization and energy loss.
Highlights
NWs have vast applications in novel logic devices, data storage, permanent magnets, sensors, and biomedicine.1–5 The higher shape anisotropy of NWs compared to their thin film and nanoparticle counterparts make them promising nanostructures for soft and hard magnetic materials
In a single domain ferromagnetic region the coercivity is proportional to d6, where d is the diameter of the grain
Depending on the wires’ diameter, either transverse wall or vortex wall can be formed during the magnetization reversal process of homogeneous NWs
Summary
NWs have vast applications in novel logic devices, data storage, permanent magnets, sensors, and biomedicine. The higher shape anisotropy of NWs compared to their thin film and nanoparticle counterparts make them promising nanostructures for soft and hard magnetic materials. Permanent magnets need to exhibit a high coercivity and energy product, while magnetic sensors require a low coercivity and hysteresis loss.. Permanent magnets need to exhibit a high coercivity and energy product, while magnetic sensors require a low coercivity and hysteresis loss.6 Such large-scale applications can be obtained by tuning the diameter, aspect ratio, and structure of the NWs. The coercivity changes strongly with the average grain size for different nanocrystalline alloys. Depending on the wires’ diameter, either transverse wall or vortex wall can be formed during the magnetization reversal process of homogeneous NWs.. Helicoidal vortex wall and transverse mode have been observed in the magnetization reversal process of isolated and first-neighbors arrays of diameter-modulated NWs.. The magnetization reversal process of a single NW and an array of NWs are demonstrated in sections II and III.
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