Multilayered Co/Cu nanowires with 10 nm diameter were fabricated as arrays in anodic aluminum oxide templates. Magnetization hysteresis (MH) loops and current perpendicular to the plane giant magnetoresistance (CPP-GMR) were measured as functions of Cu layer thicknesses. The largest CPP-GMR values (11%, or 19.5% for multilayers alone) were found in nanowire arrays that had identical MH loops whether the field was applied parallel or perpendicular to the wires. Spin transfer torque (STT) switching was measured in the 10 nm diameter nanowires and also in 60 nm diameter wires. For the 10 nm diameter nanowires, these STT curves were overlaid with small jumps (1%-2%) that were attributed to individual layers flipping and larger jumps (6.25%) that were due to collective spin flips between interacting Co layers. For larger diameter nanowires, the individual spin flips were not present, and the curves were similar to typical STT results. The current densities required to switch the Co layers from antiparallel to parallel and back (JAP-P / JP-AP) were 2.7× 108 /1.3× 108 and 3.2× 107 /-1.6× 107 A/ cm2, respectively, for the 10 and 60 nm diameter nanowires. The ability to construct large area arrays of 10 nm CPP-GMR and STT structures makes these first results exciting for eventual use in magnetic random access memory.
Bibliographical noteFunding Information:
This work was supported partially by the National Science Foundation under Award No. ECS-0621868 and the MRSEC program (Grant Nos. DMR-0212302 and DMR-0819885). The authors are grateful to Professor Randy Victora and Stephanie Hernandez for valuable discussions and also to the UMN NNIN Characterization Facility and Nanofabrication Center. They also thank Khuong Tran from Seagate for help with STT measurements.