Magnetization Reversal Process Of Magnetic Nano-point Dynamics Micromagnetic Study

Magnetic state and dynamical magnetization reversal mechanism is a key problem in preparing nanosized magnetic information devices and spin-electronic devices based on nanadots. In this thesis, based on the micromagnetic theory, the magnetic state and dynamical magnetization reversal process of rectangular magnetic nanoelements have been investigated as follows:The stable magnetic state and static magnetization reversal process of rectangular magnetic nanoelements have been studied. The results show that the magnetic state significantly depends on the initial magnetization distribution and damp coefficient. The quasiuniform C-state and S-state, vortex state, flower state are acquired by allowing the magnetization to relax from different magnetization distribution. When in large damp coefficient, the elements were found to be in the flower state. Static magnetization reversal processes of quasiuniform C-state and S-state were studied, magnetization reversal mechanism were different due to the edge domains, which result in different reversal field.The dynamical magnetization reversal process of nanoelements with initial C-state and S-state subject to square pulsed magnetic field haved been investigated. For the C-state, it was found that the reversals proceeded through different modes as the pulse amplitude is increased. For the weak magnetic field pulse, the magnetization reversal is realized through the motion of the end domain walls toward the central part of magnet and, subsequently, the formation and motion of a single vortex. As the strength of magnetic field pulse become stronger, the reversal is accomplished through the motion of the end domain walls plus the formation and motion of two vortex structure. For much stronger field pulse the reversal process is the motion of the end domain walls and subsequent formation and annihilation of several vortices. The dependence of reversal time on the field pulse amplitude displays oscillating characteristic due to the transitions of reversal modes with the field strength. For the S-state, the magnetization reversal is realized through the motion of the end domain walls toward the central part of magnet and subsequently disappearing. With the increase of the pulse strength, domain wall structure transformed from the 180°wall-like structure to 360°wall-like structure. Under a sufficient strong pulse, 360°domain walls are formed and their motion is prohibited, the reversal process is accomplished through the shrinking and disappearing of the 360°domain walls. However, a plateau is formed on the reversal time-pulse amplitude curve due to the transition of domain wall structure.The precessional magnetization reversal process and the critical switching field of magnetic nanoelements with initial C-state and S-state subject to pulsed magnetic field with different directions were investigated. The results show that with the increase of angleθ(whereθis defined as the angle between the pulsed magnetic field direction and nonodot length) , the symmetry of magnetization distribution changed, which lead to the different evolvement of magnetization distribution. For the two magnetic state, the critical switching field decreases at first, and then increases quickly as the angle increases.