Micromagnetic Study Of Magnetic Properties Of Magnetic Nanowires

Micromagnetic distribution and magnetization reversal mechanism in nanowires is an important scientific problem, and magnetic nanowire array can be used as ideal perpendicular recording media in future. In this thesis, based on the micromagnetic theory magnetic properties of nanowires have been investigated as follows:(1) The magnetization reversal mechanism of magnetic nanowires with different diameter and same aspect ratio 10 were studied by micromagnetic simulation. The results show that the magnetization reversal mechanism significantly depends on the nanowire diameter. For the smallest wire, the reversal occurs by coherent rotation;With the increase of diameter, magnetization reversal takes place via different nucleation (the transverse domain wall or the vortex domain wall) and subsequent propagation;For the larger nanowire, multidomain would form within the wire, the magnetization reversal is determined by the motion of vortexs which conform to the right hand rule. The critical diameters of different reversal mechanism are obtained. The coercivities of nanowires are calculated, the size-dependence of coercivity is interpreted in terms of reversal mechanism.(2) The change of the reversal mechanism and coercivity in nanowires arose from various defects and magnetostatic coupling among nanowires have been simulated. Difference between simulated data and experimental results is explained further.(3) Augular dependence of the coercivity Hc(θ) in magnetic nanowires with different diameter and same aspect ratio 10 were investigated by micromagnetic simulation (where θ is defined as theangle between the field direction and wire length) . The results show that Hc(9) significantly depends on the nanowire diameter, For the wire diameter smaller than the threshold diameter, the coercivity decreases as the angle increases;For the wire diameter larger than the threshold diameter;the coercivity has a peek at middle angle, and the value of angle increases with the increase of diameter. The local maximum phenomenon in small angle for the coercivity weakens as the diameter increases. The above results can be interpreted in terms of magnetization reversal mechanism. The corresponding Hc(9) of different magnetization reversal mechanism are given.(4) Micromagnetic distribution of multilayer nanowires with different size were investigated by micromagnetic simulation. There are three possible micromagnetic states in multilayer nanowires. A map of micromagnetic state for different diameter multilayer nanowires are given when the aspect ratio of ferromagnetic layer is smaller than 1(L/D < 1 ).The micromagnetic state of multilayer nanowire changes with changing nonmagnetic layer thickness.