Low frequency and weakly nonlinear spin transport in ferromagnet/insulator single and double junctions

Zheng-Chuan Wang, Qing-Rong Zheng, Gang Sua, and Bao-Heng Zhao

Department of Physics, Graduate School at Beijing, University of Science and Technology of China, Chinese Academy of Sciences, PO Box 3908, Beijing 100039, PR China

Received 1st September 2000 and Received in final form 5 December 2000

Abstract. In this paper, we apply B¨uttiker’s gauge invariant, charge conservation, nonlinear transport theory to explore the spin-polarized tunneling of ferromagnet/insulator (semiconductor) single and double junctions. The Green function of spin-polarized tunneling is calculated by the tight-binding approximation method. The energy and the angle (between the molecular field and the vertical axis) dependences of the weakly nonlinear dc transport coefficient and the linear low frequency ac transport coefficient are investigated. The ac tunneling magnetoresistance is also discussed. PACS. 75.70.Cn Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures) – 73.40.Rw Metal-insulator-metal structures – 73.23.Hk Coulomb blockade; single-electron tunneling