Enhancement of giant magnetoresistance and oscillation by wave-vector filtering in Fe/Ag/Fe/InAs/Ag

摘要

The performance of a giant magnetoresistance (GMR) heterostructure Fe/Ag/Fe/InAs/Ag(100) in the current-perpendicular-to-plane geometry is presented. Calculations are based on a realistic tight-banding model with full spd bands and the recursive Green's function algorithm. Results show that the system's GMR can reach values above 1000%. This GMR enhancement mainly is a result of the wave-vector filtering effect imposed by the InAs layer, restricting conductance within a small region around the Γ point in the 2D Brillouin zone. Calculations also reveal that when the Fermi level sits in the InAs band gap, MR gradually saturates as a function of InAs thickness with a smooth plateau; whereas when the Fermi level is in the InAs conduction band and close to the band bottom, GMR exhibits an oscillatory behavior with a large period. GMR oscillations are also observed with respect to Ag thickness, with oscillation amplitude determined by the Fermi level position relative to the InAs conduction band edge. The oscillation periods in both cases can be well explained by the concept of quantum-well states, and are determined by the spanning vector of the Fermi surface belly of the material whose thickness is varied. The observed GMR oscillations are due to the quantum interference of conduction electrons near the Γ point. The GMR and area-resistance (RA) product profiles at a wide range of Fermi energy positions relative to InAs bands are also compared. Near the GMR peak (with GMR above 1000%) in the conduction band, RA product can be as low as 8.8 Ω /μm~2. This feature of large GMR but small RA product results from the wave-vector filtering effect of doped InAs, and it makes the structure under study distinct from conventional GMR systems (small GMR, small RA) or magnetic tunnel junctions (large GMR, large RA).