Tunnel magnetoresistance in MgO-barrier magnetic tunnel junctions with bcc-CoFe(B) and fcc-CoFe free layers

Abstract

We have investigated the spin tunneling transport in magnetic tunnel junctions (MTJs) with Co40Fe40B20, Co50Fe50, and Co90Fe10 free layers which were deposited on the lower electrode consisting of the same Co40Fe40B20 reference layer/MgO barrier. The tunnel magnetoresistance (TMR) ratio depends critically on the choice of the free layer; the TMR ratios up to 355% were obtained for the MTJs with Co40Fe40B20 free layers and up to 277% with Co50Fe50 free layers, both of which have highly (001)-oriented bcc structures. No high TMR ratio was observed for the MTJs with Co90Fe10 free layer having a polycrystalline fcc structure.