| Spin-transfer effects provide a new method of manipulating magnetization states by spin-polarized current, and is promising for developing a batch of novel current-driven nano-devices. So, it has drawn high attention in academia and industry. In this dissertation, on the basis of the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation, we combine the current-driven and spin valve with tilted anisotropy. analyse the stability of magnetization states driven by spin-transfer torque in spin valve structure with tilted anisotropy and dual pinned layers structure, and discuss the effect of field-like spin-transfer torque on the current-driven magnetization dynamics. Meanwhile, we study the current-excited and adjusted ferromagnetic resonance(FMR) in spin valve structures with tilted anisotropy. The main research contents and results are given below:1. We analyse the stability of magnetization states driven by spin-transfer torque in spin valve structure with titled anisotropy. The phase diagrams defined by the magnitude and direction of spin-transfer torque are obtained by using stability analysis method. Our results show that the tilted anisotropy in the pinned layer provides a new possible choice to optimize the magnetization reversal and precession driven by current in magnetic trilayers. With the pinned-layer magnetization oriented in a certain range, one can realize different magnetic states, such as quasi-parallel and quasi-antiparallel stable states, in-plane and out-of-plane precessions, and out-of-plane stable states by varying the current. We also find that the free-layer magnetization prefers reversal for small deviation of the fixed-layer magnetization from the film plane, while precession for big deviation.2. We take stability analysis for the magnetization states driven by spin-transfer torque in spin valve with dual pinned layers theoretically. Magnetic phase diagrams are established under the control of the magnitude and direction of dual spin torques. The dynamic evolutions of magnetic states are demonstrated by solving differential equations numerically. The results suggest that the switching between different states is highly affected by the pinned-layer configurations. Selecting different pinned-layer configurations, the reversal between parallel and antiparallel orientations and the switching from stable states to precessional ones can be realized by increasing current. The reversal current is the lowest when the magnetization directions of two pinned layers are antiparallel and in the film plane. The threshold current for switching to out-of plane precession state is the lowest when the magnetization directions of two pinned layers are antiparallel and perpendicular to the film plane. For some pinned-layer configurations, there exists hysteretic switching between static and dynamic states.3. Selecting magnetic trilayers with perpendicular anisotropy for both free and pinned layers as theoretical model, we study the effect of field-like spin-transfer torque on the current-driven magnetization dynamics. The analytical expression of switching current is derived. Meanwhile, we obtain the dependence of precession frequency on the current, external magnetic field and field-like spin-transfer torque. The results show that the precession frequency of magnetization can be controlled by the current and external magnetic field. The presence of field-like spin-transfer torque can change the switching current and precession frequency.4. We investigate the current-excited and adjusted FMR in spin valve structure with a tilted polarizer and a perpendicular analyzer without external magnetic field. The analytical expression of the output dc voltage for arbitrary anisotropy in the free and pinned layers and the FMR spectra adjusted by ac frequency are derived. The results indicate that we can realize FMR throught adjusting the ac frequency without external magnetic field. The resonant location and linewidth can be adjusted by changing the pinned magnetization direction and the dc current density. In some regions defined by the dc current density and the pinned magnetization direction, the height of the resonant peak can reach maximum, i.e., resonance linewidth is smallest. To reduce the effective damping, we can appropriately select the current density and the direction of pinned magnetization. |
