Current Induced Magnetic Switching And Oscillation In Magnetic Multilayers

Since the discovery of the giant magneto-resistance, the transport of electrons and manipulation of magnetization have attracted great attentions in recent decades. We mainly study the current induced magnetic switching and oscillation in the magnetic mul-tilayers, and also discuss the configuration of local moments at the ferromagnetic (F)/antiferromagnetic (AF) interface. The dissertation consists of five chapters:In chapter one, we firstly recall a brief history of spintronics, and give an introduc-tion to the exchange bias (EB) and spin-transfer torque, and their recent development, theoretical methods.In chapter two, based on the mean-field approximation of the Heisenberg model, we study the configuration of the local moments at the F/AF interface for different interfacial coupling and magnetic anisotropy. Except for the conventional AF phase, an interfacial spin-flop phase is also found for the interfacial AF moments when the interfacial perpen-dicular coupling is dominant compared to the AF domain wall energy. In the conventional AF phase, the interfacial perpendicular coupling leads to significant enhancement of the coercivity, while in the spin-flop phase, the interfacial perpendicular coupling can con-tribute to the EB field.In chapter three, we study the effects of uniaxial spin-transfer torque (USTT) on the F as well as AF layers in EB spin valve. By analytically treating the free-energy func-tional of the F/AF bilayer and numerically solving the Landau-Lifshitz-Gilbert equation for magnetic moments, we can reproduce and explain two existing experimental facts rel-evant to USTT:One is that the EB field can be reversed by both positive and negative pulsed currents, and the other is that the critical current to excite the F moments is greatly increased in the presence of an AF layer and independent of external fields. We also de-rive the angular dependence of the critical currents to excite AF and F moments, which suggests a possible way to quantitatively determine USTT in experiments.In chapter four, we propose an array of spin-transfer oscillators (STOs) to be parallel-connected and synchronized via magnetic feedback. Based on numerically solving the Landau-Lifshitz-Gilbert-Slonczewski equation and theoretically analyzing the Kuramoto model, the cooperative dynamics of these STOs is studied in detail and the optimal orien-tation of magnetic feedback is determined. It is found that a large locked bandwidth can be obtained by simply increasing the number of coupled STOs and modulating the total phase shift of feedback signals. Specifically, for ten parallel-connected STOs, the locked bandwidth can be12times larger than that obtained from the serially connected STOs.The last chapter presents a summary and then gives some outlook for the future investigation.