Constricted current perpendicular to plane (CPP) magnetic sensor via electroplating.

Abstract

Electrochemically deposited magnetic nanowires have gained increasing attention since current perpendicular to the plane giant magnetoresistance (CPP-GMR) was observed in multilayered nanowires. Magnetic nanowires have potential for fundamental studies, including measuring spin diffusion lengths and understanding the mechanisms of the electron spin transfer. They also have great potential technological applications as CPP-GMR sensors, magnetic random access memory (MRAM), and next generation magnetic recording heads. Small diameter nanowires are desired in order to have large current density per device and a high areal density for device arrays, for example, 2 Tb/in2 media. In this research, E-beam lithography, nano-imprinting, and self-assembled nanoporous alumina templates (AAO) were studied to achieve as small diameter nanopores as possible. AAO templates with 10 nm diameter were fabricated using both Al foils and Al thin films. Very small diameter (10 nm) CPP-GMR Co/Cu nanowires were fabricated into AAO templates using electrochemical deposition. The magnetic transport properties of these multilayered and trilayered Co/Cu nanowires were investigated. It was found that nanowire anisotropies parallel and perpendicular to the nanowires were dependent on the thicknesses of Co and Cu layers. GMR of 19% was achieved with 10 nm diameter nanowires at room temperature. The magnetic free layers were as thin as 4.5 nm with GMR of 18%. Spin transfer torque switching current densities were measured to be 106 - 108A/cm2. The measurement of spin transfer torque was conducted numerous times with high repeatability in the critical switching currents from parallel to antiparallel alignment (JP-AP) and slight variations in back (JAP-P). Small resistance area products (RA) of 0.003 ohmµm2 were achieved with trilayers that had 40ohm total resistance. All of results in this study show that nanowires with 10 nm diameters have potential application as next generation CCP-GMR sensors and spin transfer torque MRAM.