Research On Ferromagnetic Resonance, Reversal And Oscillation In Magneitc Tunnel Junction With Perpendicular Anisotropy

Spintronics becomes a hot research topic in recent years and it has extensively been applied in industries. The theory predicted the existence of spin-transfer-torque (STT) effect in 1996. And it was quickly confirmed by the experiment. The research based on STT is rapidly developed into a hotspot in international magnetic field. STT effect also becomes another major discovery in the field of spintronics after the giant magnetoresistance (GMR) effect. Based on STT effect, the magnetization vector can be driven in ferromagnetic thin films only by injecting current. Thus we can obtain a simple and reliable solution to write data in MRAM.In this paper, we study the dynamical properties of magnetization in the free layer of magnetic tunnel junction (MTJ) through theoretical analysis and computer simulation. The theoretical guidance is provided for practical application of the spin torque nano-oscillator (STO) and MRAM. Through comparing the critical current and the time of the magnetization reversal with changing the magnetization vector direction in the pinned layer and the current in the free layer, we provide a reasonable solution to reduce the reversal time of MRAM and improve the oscillation frequency of the nano-oscillator.The work can be summarized as follows:Firstly, the magnetic properties of nanodevices with STT effect are introduced under current driving. Also, we show their research background, research significance, and prospects.Secondly, we researched ferromagnetic resonance in MIJ with perpendicular anisotropy. Through Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation, the dependence of the external magnetic field, the microwave frequency, the STT, field-like torque and the space magnetic permeability are obtained. And the magnetic resonance spectrum is also got. By changing the magnitude of current density, we can control the STT. We can adjust the resonance line-width of the magnetic resonance spectrum and the resonance frequency by changing the magnitude of current density, magnetic field, microwave frequency and the ratio of the STT with field-like torque. The effective damping of the system can be minimized through adjusting their relationship.Thirdly, based on the macrospin model, LLGS equation is obtained in spherical coordinates. By the analysis to various components of the LLGS equation, we explain the dynamics features of the magnetization vector under current driving.Fourth, we study the reversal mechanism of MRAM in MTJ structure with perpendicular magnetic anisotropy and give factors that how to improve the magnetization vector reversal time. At the same time, we study the dual memory of the fixed layers with the spin-Hall effect.Fifth, we study the oscillation mechanism of STO composed of MTJ with in-plane magnetic anisotropy in free layer and out of plane magnetic anisotropy in fixed layer. The amplitude of oscillation is obtained by LLGS equation and the oscillation frequency is obtained by Fast Fourier Transform. We find out some new properties of the oscillator, and give explanation by analyzing the energy.