scholarly journals CPP-GMR Performance of Electrochemically Synthesized Co/Cu Multilayered Nanowire Arrays with Extremely Large Aspect Ratio

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 5
Author(s):  
Himeyo Kamimura ◽  
Masamitsu Hayashida ◽  
Takeshi Ohgai

Anodized aluminum oxide (AAO) films, which have numerous nanochannels ca. 75 nm in diameter, D and ca. 70 µm in length, L (ca. 933 in aspect ratio, L/D), were used as a template material for growing Co/Cu multilayered nanowire arrays. The multilayered nanowires with alternating Cu layer and Co layers were synthesized by using an electrochemical pulsed-potential deposition technique. The thickness of the Cu layer was adjusted from ca. 2 to 4 nm while that of the Co layer was regulated from ca. 13 to 51 nm by controlling the pulsed potential parameters. To get a Co/Cu multilayered nanowire in an electrochemical in-situ contact with a sputter-deposited Au thin layer, the pulsed potential deposition was continued up to ca. 5000 cycles until the nanowire reached out toward the surface of AAO template. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ca. 23.5% at room temperature in Co/Cu multilayered nanowires with ca. 3500 Co/Cu bilayers (Cu: 1.4 nm and Co: 18.8 nm). When decreasing the thickness of Co layer, the CPP-GMR value increased due to the Valet–Fert model in the long spin diffusion limit.

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 218
Author(s):  
Saeko Mizoguchi ◽  
Masamitsu Hayashida ◽  
Takeshi Ohgai

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.


2013 ◽  
Vol 50 (10) ◽  
pp. 201-206 ◽  
Author(s):  
T. Ohgai ◽  
N. Goya ◽  
Y. Zenimoto ◽  
K. Takao ◽  
M. Nakai ◽  
...  

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5887-5894 ◽  
Author(s):  
HONG GUE SHIN ◽  
JONG TAE KWON ◽  
YOUNG HO SEO ◽  
BYEONG HEE KIM

A simple method for the fabrication of polymer master for antireflective surface is presented. In conventional fabrication methods for antireflective surface, coating method with low refractive index have usually been used. However, it is required to have a high cost and a long processing time for mass production. In this paper, antireflective surface was fabricated by using hot embossing process with porous anodized aluminum oxide. Through multi-AAO and etching processes, nano patterned master with high aspect ratio was fabricated at the large area. Size and aspect ratio of nano patterned master are about 175 ± 25 nm and 2 ~ 3, respectively. In order to replicate nano patterned master, hot embossing process was performed by varying the processing parameters such as temperature, pressure and embossing time etc. Finally, antireflective surface can be successfully obtained after etching process to remove selectively silicon layer of AAO master. Optical and rheological characteristics of antireflective surface were analyzed by using SEM, EDX and spectrometer inspection. Antireflective structure by replicating hot embossing process can be applied to various displays and automobile components.


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