Micromagnetic Studies Of Spin Dynamics In Magnetic Tunnel Junction

In recent years, giant magnetoresistance (GMR), tunnel magnetorestance (TMR) and spin transfer torque (STT) effect have attracted considerable attention since they have potential applications in the magnetic random access memory, racetrack memory and microwave oscillators. In this thesis, we investigated Spin Dynamics in magnetic tunnel junction via micromagnetic simulations. The main contents are as follows:The 360°domain wall motion driven by current perpendicular to the magnetic plane was simulated. The dependences of 360° domain wall velocity on the current density with different parameters are shown, and the difference between Slonczewski torque effect and fieldlike torque is analyzed in detail. The behaviors of 360° domain wall are shown by Lagrangian formalism. In addition, we provide a new type of current perpendicular to the magnetic plane magnetic tunnel junction with many 360° domain walls, which is designed to achieve local current, for driving the single 360° domain wall. The local spin polarized current introduced can drive single 360° domain wall.For magnetic system, the introduction of Dzyaloshinskii-Moriya interaction (DMI) can lead to curious phenomena. A new type of skyrmion-like spin texture,2π-vortex is obtained in a thin nano-disk with Dzyaloshinskii-Moriya interaction. We have simulated the existence of 2π-vortex by energy minimization method. Furthermore, the spin polar-ized current is introduced in order to drive the motion of 27r-vortex in a nano-disk with diameter 140 nm. When the current density matches with the current injection area, 2π-vortex soon reaches a stable precession. The relationship between the precession frequency of 2π-vortex and the current density is almost linear.In a magnetic tunnel junction, a free layer with in-plane magnetic anisotropy ex-hibits a higher stability. We have investigated magnetization reversal of magnetic tunnel junction with different magnetic anisotropies assisted by microwave field. Simulation-s show that natural ferromagnetic resonance frequency increases with the increasing magnetic anisotropy constant. The critical current density of the magnetization switch can be reduced in the memory cell with in-plane magnetic anisotropy by microwave-assistance. The magnetization switching mechanism shows some new features due to the introduction of in-plane magnetic anisotropy.