Micromagnetic Research Of Spin Torque Nano-oscillator

In recent years, spin transfer torque (STT) effect has attracted considerable attention since the magnetization can be effectively manipulated by spin polarized current in the magnetic thin film. STT has possessed potential applications in the magnetic random access memory (MRAM) and microwave oscillators. In this thesis, we investigated Spin torque nano-oscillator via micromagnetic simulations. The main contents are as follows:(Ⅰ) Oscillation of magnetic vortex investigated by micromagnetic(1) In one single magnetic disk, the gyrotropic frequency can be obviously affected by the parameters of magnetic materials. The results indicate that the gyrotropic frequency decreases with the increasing of the radius of disk, meanwhile, increases with the increasing of exchange interaction constant.(2) For the vertical structure of double disks, the magnetostatic energy decreases with the increasing of disk space. We investigated different polarization and chirality configurations in a pair of vortex-state disks. When the magnetic vortex have the same polarity, the Micromagnetic simulation results show that the gyrotropic frequency increases with the increasing of disk space. When the magnetic vortices have different polarity, the gyrotropic frequency is split into two gyrotropic frequency peaks.(Ⅱ) Phase locking dynamics of coupled vortex-based spin transfer oscillators(1) The phase locking time can be effectively reduced by decreasing the disk space.(2) The exchange interaction can not only reduce the phase lock time effectively, but also influence the phase differences value. (Ⅲ) The influence of annular impurities in the vortex dynamics(1) The annular impurities can influence the precession radius of the magnetic vortex. With a small polarization current density, the precession radius increases with the increasing of the radius of the ring. As the polarization current density becomes large, the precession radius decreases firstly and increases afterward with the increasing of the radius of the ring. Also, we investigated the influence of the vortex precession by variation of the width of the ring. The results indicate that the precession radius decreases with the increasing of the radius of the ring.(2) The precession radius can be effectively improved by the exchange interaction, under the same current density.(IV) Skyrmion motion in nanodiskIn this section, we investigated the motion of magnetic skyrmion with the vortex-like states in a nanodisk. It is found that spin polarized current can drive skyrmion steady-state oscillations, and the precession radius of skyrmion increases with increasing of the current density and the DM (Dzyaloshinsky-Moriya) parameter D. We also investigated the skyrmion dynamics in a nanodisk with antidots. The simulation results indicate that skyrmion can move around the antidot and keep steady-state oscillations in the nanodisk with the proper current density. Moreover, we have noticed that the diameter of skyrmion will be changed as the trajectory of skyrmion moving around the antidot.