Research On Synthesis And Simulation Of Magnetic Nanostructures

In recent years, magnetic nanostructured materials have attracted much attention for their light weight, unique shape anisotropy and high specific surface area. These materials show potential applications in magnetic storage, sensor, microwave absorber and microwave devices.In the first part of this thesis, the interaction fields of Co nanowire arrays have been investigated by micromagnetics simulation software(OOMMF). Numerical values of interaction field between nanowires have been obtained by analyzing their First Order Reversal Curves(FORC). The results show that due to the inhomogeneous interaction field, the magnetization reversal process of each nanowire is asynchronous. Besides, the interwire interaction field is found to weaken the magnetic anisotropy along the direction of length.In addition, the effects of Co nanotube geometrical size(length, inner diameter and outer diameter) and magnetocrystalline anisotropy on the high frequency permeability dispersion behaviors have been studied. The results show that the nanotube’s length determines the location of resonance peak with higher frequency in the simulated magnetic spectra. However, the inner diameter determines the location of magnetic resonance peak with lower frequency. Furthermore, the direction of magnetocrystalline anisotropy can affect the main natural resonance peak. Finally, we have simulated the high frequency magnetic spectra of nanotube array with different magnetic remanent states by applying different external fields on nanotube arrays and removing the applied field. The results show that the number of resonance frequency and the intensities of resonances are strongly affected by the remanent states. The above results indicate that without changing the magnetic nanostructured materials, we can tune the high frequency permeability spectra by controlling the number of nanotubes, the interspacing of nanotubes, the geometric dimensions and the remanent states.In the second part of this thesis, Fe-based magnetic nanostructured materials have been synthesized in anodic aluminum oxide(AAO) nano templates by electrochemical deposition. The morphologies, crystalline states, compositions and magnetic properties have been discussed. The experimental results show that Fe nanowire arrays have high aspect ratio and obvious magnetic anisotropy. The easy direction of magnetization is along the direction of length. The as-prepared Fe-P amorphous nanowire arrays also show obvious magnetic anisotropy. The easy direction of magnetization is along the direction of length. However, in the case of magnetic nanotube array of Fe, the easy direction of magnetization is perpendicular to the length of nanotubes. For Fe-P nanotube array, there are two magnetic phases coexist, α-Fe phase and amorphous phase. The Fe-P nanotube array shows a weak magnetic anisotropy. The experimental results indicate that the easy direction of magnetization in a nanostructured material is a consequence of the following factors: interactions between nano elements, the shape anisotropy, geometry and crystalline states.