Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic aluminum rod. The nanochannel diameter D and length L were about 60 nm and 60 mu m, respectively. The aspect ratio L/D reached similar to 1000. A rectangular pulsed potential deposition technique was applied to electrochemically grow the multilayered nanocylinders with alternating Cu and Co thin layers in the AAO nanochannels. The Co/Cu bilayer thickness was decreased to around 7 nm at the minimum by controlling the pulsed potential and duty cycle during the electrodeposition process. An electrochemical in situ single contact process was demonstrated by monitoring the observed current until a Co/Cu multilayered nanocylinder reached the nanoporous Au film on the AAO thick film. The resistance of the Co/Cu multilayered nanocylinder was determined to range from 1 to 2 k Omega, which corresponded well with a theoretical estimation. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of a Co/Cu multilayered nanocylinder with similar to 6000 bilayers (Cu = 2.4 nm, Co = 7.1 nm) reached up to 31.5% at room temperature. Valet-Fert model agreed well with the present study concerning the effect of Cu-layer thickness on CPP-GMR.

Automated summary

In this study, an anodized aluminum oxide (AAO) thick film with nanochannels was successfully synthesized using a cathodic exfoliation technique, followed by the electrochemical growth of multilayered nanocylinders with alternating Cu and Co thin layers in the nanochannels. By controlling the pulsed potential and duty cycle, the Co/Cu bilayer thickness was reduced to around 7 nm, leading to a current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) reaching up to 31.5% at room temperature for Co/Cu multilayered nanocylinders with approximately 6000 bilayers. The Valet-Fert model was found to be consistent with the experimental results regarding the effect of Cu-layer thickness on CPP-GMR.