Study On Magnetic Moment Dynamics Of Single Magnetic Particles

Studying the magnetization reversal of the magnetic materials is a very importantsubject because of its widely use in the magnetic storage devices, and it is closely relatedto our daily lives. Now with the rapid development of information age, the storage densityand speed of the storage is more and more difficult to meet the needs of people. So thestorage technology of high density and speed need the continuous development. The realmagnetic moment reversal is a very complicated process, thus we should use the simplifiedmodel to study it to save time and also bring good guidance to the practical application. Inthis thesis, the magnetization reversal dynamics was studied. The magnetic momentreversal of the single-domain particle in the uniaxial model was discussed from twoaspects. The structure of this article is as follows:The first chapter is the introduction of the background and development of this fieldby interpreting existing references.The2ndchapter is the theory of our work. In this part we have a introduction of theLandau-Lifshitz-Gilbert equation and the spherical coordinates form of it. Also the LLGequation with the spin transfer torque item was introduced.In chapter3, we have discussed the magnetization reversal under the time dependentmagnetic field. The dynamics can be described by the Landau-Lifshitz-Gilbert equation.From this equation, both the analysis and numerical methods were used for studying themagnetization reversal of the Stoner particle. When use a sinusoidal variational magneticfield as the external field (like electromagnetic wave or laser), there existed a fixed ratiobetween the amplitude and frequency of the external field to maintain the reversal timeequal to one half period of the applied field. Then we used the continuous pulsed rectifiedmagnetic field pulse as the external field. Thus one can conveniently decrease theamplitude or increase the reversal speed by adjusting the number of the pulses.STT-induced magnetization reversal was discussed in chapter4. The stationary-statesolutions of magnetization dynamics under a spin-polarized current that was polarized inan arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxialmagnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to threepairs of magnetization equilibrium states existed, depending on the current intensity andthe direction of the spin polarization. By numerically analyzing the stabilities of theseequilibrium states, the threshold switching current for the reversing the magnetic vectorwas obtained under different current polarization configurations, which may be useful foruse in future spintronics devices.The last chapter is the conclusion of this article. And some leftover problems were putforward. We also give some outlooks at last.