Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio

Effect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameterD∼67 nm and length L∼70 μm. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L/Dof ∼1,045, were fabricated in theAAOMnanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co2+,Ni2+ and Cu2+ ions. Co–Ni/Cu alternating structure with Co84Ni16 alloy layer-thickness of 9.6 nmand Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L/D. InCo84Ni16/Cu multilayered nanocylinders, the coercivity and squareness were∼0.46 kOe and∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co84Ni16/Cu multilayered nanocylinders

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

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

Microhardness and heat-resistance performance of ferromagnetic cobalt-molybdenum nanocrystals electrodeposited from an aqueous solution containing citric acid

Using a potentiostatic electrodeposition technique, nanocrystalline cobalt-molybdenum (Co-Mo) superalloys containing molybdenum oxide (MoOX) were synthesized from an aqueous solution containing citric acid. Molybdenum content in the alloys was controlled up to approximately 53% by adjusting the cathode potential during the alloy electrodeposition. Based on theXRDprofiles and electron diffraction patterns, an amorphous-like nanocrystalline structure was observed in the alloys with high molybdenum content. XPS analysis revealed that the chemical state of electrodeposited molybdenum was almost metallic and the oxide state was also detected partially. According to the magnetization curves, the coercivity of electrodeposited Co-Mo alloys decreased down to approximately 72 Oe with increasing the molybdenum content up to around 53%. The microhardness reached 845 kgfmm−2 in the electrodeposited Co-53%Mo alloy and greatly exceeded that of pure cobalt (ca. 250–300 kgfmm−2). Heat resistance performance of the electrodeposited nanocrystalline Co-53%Mo alloy was improved by theMoalloying effect because the recrystallization and oxidation behavior were not observed even if the annealing temperature was increased up to 700 °C

Structure of corrosion product formed on carbon steel covered with NiSO4-Added resin coating under sulfuric acid mist environment containing chloride

Corrosion resistance of carbon steel covered with resin coating containing nickel sulfate has been evaluated under chloride and sulfuric acid mist environment. The structure of corrosion products formed on steel surface was investigated by XRD and XAFS analyses using synchrotron radiation. Nickel sulfate promoted the formation of goethite and akaganeite. It was considered that this akaganeite was not tetragonal β-FeOOH but monoclinic akaganeite containing nickel.Shota Hayashida, Masamitsu Takahashi, Hiroshi Deguchi, Hiroaki Tsuchiya, Koushu Hanaki, Masato Yamashita, Shinji Fujimoto, Structure of Corrosion Product Formed on Carbon Steel Covered with NiSO4-Added Resin Coating under Sulfuric Acid Mist Environment Containing Chloride, Materials Transactions, 2021, Volume 62, Issue 6, Pages 781-787, Released on J-STAGE May 25, 2021, Advance online publication May 14, 2021, Online ISSN 1347-5320, Print ISSN 1345-9678, https://doi.org/10.2320/matertrans.C-M2021819

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

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

Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio

Effect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameter D ∼67 nm and length L ∼70 μ m. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L / D of ∼1,045, were fabricated in the AAOM nanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co ^2+ , Ni ^2+ and Cu ^2+ ions. Co–Ni/Cu alternating structure with Co _84 Ni _16 alloy layer-thickness of 9.6 nm and Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L / D . In Co _84 Ni _16 /Cu multilayered nanocylinders, the coercivity and squareness were ∼0.46 kOe and ∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co _84 Ni _16 /Cu multilayered nanocylinders

Microhardness and tensile strength of electrochemically synthesized nickel-cobalt binary alloy sheets exfoliated from a dumbbell-shaped titanium cathode

Nanocrystalline nickel–cobalt (Ni–Co) binary alloy sheets were fabricated through electroforming in an acidic aqueous bath using exfoliation from a metallic titanium cathode. Cobalt content in Ni–Co alloy sheets ranged from 28.8 at% to 72.0 at% depending on experimental parameters, such as cathodic overpotential and bath composition. The surface roughness ( R _a ) of the electroformed alloy sheets significantly decreased down to 1.5 μ m as saccharin sodium dihydrate was added as an additive to the acidic aqueous solution bath. X-ray diffraction profiles and transmission electron microscopy images indicated that the electroformed Ni–Co alloy sheets have a nanocrystalline structure (grain size ≈ 30 nm). The lattice constant of the electroformed Ni–Co alloy sheets increased with an increase in cobalt content (i.e. solute atom concentration). The mechanical properties were significantly improved because of the synergistic effects of crystal grain refinement and solid solution strengthening. The microhardness and tensile strength of the electroformed Ni–Co alloy sheets reached 609 kgf mm ^−2 and 1757 MPa ( X _Co = 49.9 at%), respectively. The tensile strength of the electroformed Ni–Co alloy sheets in this study significantly exceeded that of solidified Ni–Co alloys (approximately 370 MPa). Therefore, this study offers a technique to enhance the mechanical properties of electroformed Ni–Co alloy sheets