Magnetoresistance in Ferromagnet/Semimetal/Ferromagnet Junctions

Abstract

Electrical conductance and magnetoresistance (MR) in ferromagnet (FM) junctions with a nonmagnetic (NM) spacer are calculated within the ballistic limit for the current perpendicular to the junction planes. Emphasis is placed on the roles of the electronic states of the NM spacer in the MR. The MR shows a maximum when the electronic structure of the NM spacer changes from semimetallic to semiconductive. The enhancement of the MR ratio is attributed to a distinct change in the partial density of states of the FM leads at the interfaces of the junction. An important ingredient governing the MR ratio is the spin dependence in the matching of the Fermi surfaces between FM leads and the NM spacer. The roles of realistic electronic structures and the roughness of the junctions in MR are also discussed.