Giant MR Ratio by Using Metastable bcc-Cu Spacer Layer in Epitaxial Current In-Plane Giant Magnetoresistance Devices

摘要

Current in-plane giant magnetoresistance (CIP-GMR) has been used in magnetic sensorapplications because it has low noises, adjustable resistance and almost no bias voltagedependence of MR ratio. However, its magnetoresistance (MR) ratio has been saturated forlong years although larger value is necessary to increase the signal output for various magneticsensor applications. It is well known that good lattice and band matchings are necessary toobtain large MR ratio. Since previous study shows ideally perfect lattice match on bcc-Fe/bcc-Cu/bcc-Fe because of the formation of metastable bcc-Cu spacer, it is worth to investigateepitaxial bcc Co_(1-x)Fe_x-based CIP-GMR spin valves with thin Cu spacer. The stacking of MgOsubs./Co_(1-x)Fe_x/Cu/Co_(1-x)Fe_x/IrMn/Ta were deposited by sputtering with x = 10, 25, 50, 67 and100. We found a large enhancement of MR ratio from 4% in pure Fe (x = 100) to over 20% inbcc-CoFe (x = 25-67) as shown in Fig.1. The largest observed MR ratio of 26% in Co_(50)Fe_(50) isclose to the highest ever reported value (28%). We also fabricated antiferromagneticallyexchange coupled MgO subs./Co_(50)Fe_(50)/Cu/Co_(50)Fe_(50)/MgO GMR stack, where the MgO cappinglayer is to introduce a specular reflection of conduction electron at the interface with CoFe. Asa result, we observed giant MR ratio of 40% which is the highest MR in trilayer CIP-GMR everreported. As shown in Fig.2, our TEM analysis confirmed Co50Fe50 and Cu layers coherentlyconnected without any dislocation because of the formation of bcc Cu spacer as previouslyreported in Fe/Cu/Fe stack. Our first principle calculation confirmed the improvement ofband matching with bcc Cu from Fe to Co50Fe50 is the origin for observed giant MR ratio.