Synthesis And Magnetic Properties Of Nanowires And Nanotubes

In view of the quasi one-dimensional magnetic nanomaterials have huge potential applications as ultra-high density magnetic recording media, we use electrochemical and sol-gel methods of preparation and characterization of the alloy nanowires, oxide nanowires and nanotubes, the use of micromagnetic simulation method and the view of magnetic charge to study the magnetization reversal mechanism of nanowire and their arrays, using micromagnetic simulation to investigate the magnetization reversal mechanism of nanotube. The main results are as follows:1. Preparation and magnetic properties of the alloy nanowires:The electrochemical methods were employed to prepare Fe100-xMox (13≤x≤25) alloy nanowire arrays. X-ray diffraction results show that the crystal structure of Fe100-xMox alloy nanowires gradually changes from polycrystalline phase to amorphous phase with the increase of Mo content, diffraction peak shifted to the left gradually increased, the maximum offset angle of Fe80Mo2o nanowires is about0.4°when Mo content reaches20at.%, and its reason due to the increase of lattice constant of Fe100-xMox alloy nanowires. The magnetic measurement results display that with increasing of Mo content, the magnetic hysteresis loops of Fe100-xMox alloy nanowires in parallel to the axis of nanowire are not rectangular and the slopes of magnetic hysteresis loops are increased, the coercivity and remanence ratio are decreased, indicating that the magnetostatic interactions between nanowires and the magnetocrystalline anisotropy both have significant influences on the magnetization reversal process of nanowire arrays.2. Preparation and magnetic properties of the oxide nanotubes and nanowires:We used the sol-gel method to prepare CuFe2O4nanotube arrays with different diameters. The measurements of magnetic properties indicate that CuFe2O4nanotube arrays with outer diameter of200nm exhibit the magnetic anisotropy with the easy magnetization direction along the axis of nanotubes. It illustrates that the magnetic anisotropy mainly results from the shape anisotropy. The use of sol-gel method prepared NiO nanotube arrays which showed room temperature ferromagnetism. Surface effect especially uncompensated surface spin magnetism is presumed to dominate ferromagnetism. NiO and CO3O4nanowire arrays were prepared via the electrochemical methods in the aqueous solution or the solution of dimethylsulfoxide (DMSO) followed by heat treatment process, respectively.3. The magnetization reversal mechanism of the nanowire and their arrays:Micromagnetic simulation results show that the magnetization reversal process of nanowire is the magnetic moment of both ends of nanowire flipping at the same time, the formation of the magnetization reversal of nuclear on side, two magnetization reversal nucleus change into four magnetization reversal nucleus, and then propagates through the whole nanowire. In the same aspect ratio of nanowire with the diameter increases, the coercivity decreased. The magnetization reversal process of nanowire arrays is nanowire at a different location in nanowire arrays gradual rollover occurs, and ultimately realized the flipping of nanowire arrays. Compared to non-defect nanowires, the interaction between nanowires reduce in defective nanowires, the flipping order of the different position of nanowires change, the coercivity of the array system increase. According to the simulation results, construct theoretical models of asymmetric magnetization reversal; by the view of magnetic charge found that nanowires may be non-uniform magnetization mechanism.4. The magnetization reversal mechanism of nanotube:Micromagnetic simulation results show that if the aspect ratio and the ratio of inner to outer diameter of nanotube are all the same, the coercivity decreased with increasing of the outer diameter of nanotube. In case of the aspect ratio and the outer diameter of nanotube are all the same, the coercivity first decreases and then increase with the increase in the inner diameter of nanotube. The change of the length and the inner as well as outer diameter of nanotube which varying the shape anisotropy of nanotube, thus affecting the magnetization reversal process of nanotube, and then change the coercivity of nanotube. When the outer diameter of nanotube greater than40nm, a two flip exist in the magnetization reversal process of nanotube, before the first switching, the distribution of magnetic moment of nanotube at both ends are all the vortex-like structure, magnetic moment of the middle part of nanotube are arranged along the axis of nanotube. Before the second switching, the distribution of magnetic moments of the middle part of nanotube is the vortex-like structure, magnetic moment of the rest of nanotube have been flipped and still arranged along the axis of nanotube.