报告题目：Ac engineering of spin transfer torques in magnetic tunneling junctions

报 告 人：陈晓彬，McGill University

报告时间：2016年6月8日10：00

报告地点：理科楼三楼报告厅（C302）

报告摘要：Phenomena of spin transfer torques (STTs) have been attracting persistent interests due to promising prospects of STTs in designing nano devices. By using nonequilibrium Green's function method, we derive time-averaged formulism for spin transfer torques in a noncollinear magnetic tunneling system under ac modulation within wide-band-limit approximation. Using these formulas, we further investigate ac spin transfer torques in a carbon-nanotube-based magnetic tunneling system. It shows that under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the regular angular dependence on noncollinear angle is maintained. By introducing photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced by about 10 and 80 times, respectively. Further analysis shows that optimized enhancement can be achieved by using ac driving frequency w=e0/k, k=1,2,..., where e0 marks a remote dc transmission peak, and using ac amplitude D such that D/w maximizes a kth-order Bessel function of the first kind. Out findings suggest that ac modulation is a promising way for electrical manipulation of spin transfer torques, paving the road towards emerging nanoelectronic and spintronic devices utilizing spin transfer torques.