The Theoretical Research About The Tunneling Magnetoresistance In Double Spin Filter Tunnel Junctions

Recently, with the application and development of the nano-technology, the research about the spin-polarized electron transport has become an important field in condensed matter physics. In this thesis, some topics in tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) have been reviewed and studied.In this thesis, the first part is the background knowledge and the current development in theoretical and experiment fields about the spin-dependent tunneling magnetoresistance. In the second part, the tunneling conductance and tunneling magnetoresistance in a new type of double spin filter tunnel junction are studied. This new type double spin filter tunnel junction consists of two ferromagnetic insulators (semiconductors) layers separated by a nonmagnetic insulator (NI) layer and can be simply represented by NM/FI/NI/FI/NM (Here NM represent the nonmagnetic metal layer, FI and NI represent the ferromagnetic insulators (semiconductors) layer and the nonmagnetic insulators (semiconductors) layer respectively). Comparing with the NM/FI/FI/NM double spin filter junction, this kind of double spin filter tunnel junction is developed by inserting a new NI layer between two FI layers. The purpose of inserting new NI layer is to decrease the interlayer exchange coupling between two FI layers, which would have disadvantage effects on the TMR and sensitivity of the double spin filter junctions. Our theoretical results show that, for the NM/FI/NI/FI/NM type double spin filter tunnel junctions, the large TMR can be obtained by adjusting the thickness of the middle NI layer. In...