Determination of Cobalt Spin-Diffusion Length in Co/Cu Multilayered Heterojunction Nanocylinders Based on Valet–Fert Model

Abstract

Anodized aluminum oxide (AAO) nanochannels of diameter, D, of ~50 nm and length, L, of ~60 µm (L/D: approx. 1200 in the aspect ratio), were synthesized and applied as an electrode for the electrochemical growth of Co/Cu multilayered heterojunction nanocylinders. We synthesized numerous Co/Cu multilayered nanocylinders by applying a rectangular pulsed potential deposition method. The Co layer thickness, tCo, ranged from ~8 to 27 nm, and it strongly depended on the pulsed-potential condition for Co layers, ECo. The Cu layer thickness, tCu, was kept at less than 4 nm regardless of ECo. We applied an electrochemical in situ contact technique to connect a Co/Cu multilayered nanocylinder with a sputter-deposited Au thin layer. Current perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ~23% in a Co/Cu multilayered nanocylinder with ~4760 Co/Cu bilayers (tCu: 4 nm and tCo: 8.6 nm). With a decrease in tCo, (ΔR/Rp)−1 was linearly reduced based on the Valet–Fert equation under the condition of tF > lFsf and tN < lNsf. The cobalt spin-diffusion length, lCosf, was estimated to be ~12.5 nm.

Modulated critical currents of spin-transfer torque-induced resistance changes in NiCu/Cu multilayered nanowires

“…Spin-transfer torque (STT) has been utilized as an effective tool in fundamental studies [1,2] as well as advanced technologies [2][3][4][5][6] to quickly change the magnetization in nanoscopic magnetic systems [2,5,7]. Among manifold material synthesis strategies, high-aspect-ratio multilayered nanowire arrays based on anodic aluminum oxide (AAO) template-assisted electrodeposition has attracted wide interest because of its low cost as well as high flexibility on tailoring the magnetic properties of magnetic systems and thus STT effects [8][9][10][11][12]. Moreover, it enables a larger number of free layers, whose magnetization can be flipped by STT [10] in one nanowire [9,11].…”

“…Among manifold material synthesis strategies, high-aspect-ratio multilayered nanowire arrays based on anodic aluminum oxide (AAO) template-assisted electrodeposition has attracted wide interest because of its low cost as well as high flexibility on tailoring the magnetic properties of magnetic systems and thus STT effects [8][9][10][11][12]. Moreover, it enables a larger number of free layers, whose magnetization can be flipped by STT [10] in one nanowire [9,11]. Comparing with the classical trilayer system (including one hard layer with fixed magnetization, one free layer, and one nonmagnetic spacer layer in between) [10], the presence of more free layers enhances, for example, the magnetoresistance (MR) [7,13] and ferromagnetic resonance modes [14,15].…”

Applications and Properties of Magnetic Nanoparticles

“…Co/Cu multi-layered nanocylinders, electrodeposited into anodized aluminium oxide nanochannels, were synthesized and characterized by Mizoguchi and co-workers [ 8 ]. The nanocylinders showed high current-in-plane giant magnetoresistance performances and a cobalt spin–diffusion length that can be described by Valet–Fert equation.…”