Co Cu Layer Research Articles

Magnetotransport Mechanism of Individual Nanostructures via Direct Magnetoresistance Measurement in situ SEM.

The accurate magnetoresistance (MR) measurement of individual nanostructures is essential and important for either the enrichment of fundamental knowledge of the magnetotransport mechanism or the facilitation of desired design of magnetic nanostructures for various technological applications. Herein, we report a deep investigation on the magnetotransport mechanism of a single CoCu/Cu multilayered nanowire via direct MR measurement using our invented magnetotransport instrument in situ scanning electron microscope. Off-axis electron holography experiments united with micromagnetic simulation prove that the CoCu layers in CoCu/Cu multilayered nanowires form a single-domain structure, in which the alignment of magnetic moments is mainly determined by shape anisotropy. The MR of the single CoCu/Cu multilayered nanowire is measured to be only 1.14% when the varied external field is applied along the nanowire length axis, which matches with the theoretical prediction of the granular film model. Density functional theory calculations further disclose that spin-dependent scattering at the interface between magnetic and nonmagnetic layers is responsible for the intrinsic magnetotransport mechanism.

Electrodeposited CoCu/Cu meta-conductor with suppressed skin effect for next generation radio frequency electronics

Multilayered Cu/CoCu metal-conductors were prepared by alternatively electrodepositing Cu and CoCu layers in the same electrolyte. The relationships between the phase structure, surface roughness, magnetic properties and the plating potential have been studied in details. Soft CoCu layers with low coercivity were obtained by selecting proper additives, which allowed the introduction of in-plane uniaxial magnetic anisotropy and negative permeability above 1.5 GHz. A transmission line consisting of 10 CoCu/Cu bilayers with near zero effective permeability was then designed and fabricated, which yielded >80% lower resistance at 10 GHz compared to a Cu transmission line in the same dimensions. This study offers a novel metal-conductor with suppressed eddy current loss and a low-cost method for next generation RF electronics.

Porous Co-Cu Electrode Fabricated By Electroplating through Sacrificial Glass Fiber Paper Template

Due to the over-fertilization and runoff, an increased phosphate concentration in natural water systems often results in serious environmental problems such as eutrophication and harmful algae blooming. In order to protect drinking water resources, online phosphate sensors for real-time monitoring of the exact phosphate level in natural water body are highly demanded. Compared with traditional method such as liquid chromatography-mass spectrometry (LC-MS) which involves complex facilities and process, various types of environmental microsensors have already shown great potential in terms of simplified test procedures, fast response and in-situ­ measurement capability. However, there exist technical challenges such as complex fabrication processes, instability, and oxygen interferences for practical implementations. Among these works, a cobalt-coated needle type phosphate potentiometric sensor was reported before by one of authors[1]. A sensing mechanism was proposed for a theoretical explanation of pH effect, potential shift and oxygen interference of Co electrode, which also pointed out a direction for improving the sensor performance for real environment application[1, 2]. Another study reported that alloying a different metal element inert to phosphate could stabilize the sensor electrode by affecting redox reaction and reducing the over activity of Co[3]. However, since this sensor is based on potentiometry, oxygen interference still exists during measurements. Enlightened by this work and electrochemistry knowledge[4], we seek to employ an amperometric technique by shifting the electrode surface redox reaction to eliminate oxygen interference. We designed and fabricated a textured, amperometric Co-Cu microelectrode using pulsed-electroplating(PEP)[5] through sacrificial glass fiber paper template and characterized the sensor for in situ phosphate monitoring. The sensor fabrication process starts from photolithography electrode patterning on Au/Ti/SiO2 coated silicon substrate. A glass fiber filter paper (0.5μm pore size) was attached to the patterned Au electrode surface as a template and fixed by two glass plates. One end of glass fiber paper was dipped in an electrolyte (CoSO4, CuSO4). While the whole paper was soaked, a pulsed potential (duty cycle=0.5) was applied. During the electroplating process, the electrolyte was supplied continuously to electrode surface by a capillary effect so that Co-Cu electrode surfaces might conform to the texture of the paper template. After the PEP process, the electrode was dipped in a buffered oxide etchant to remove the glass fiber filter paper leaving behind a porous Co-Cu layer on the electrode. Potentiometric tests were conducted first to confirm the electrode response to phosphate. The Co-Cu electrode responded immediately (< 30s) when phosphate was present in buffered solution (25 mM KHP, pH 4.0) with a sensitivity of -34mV per decade. Then we explored the electrode’s electrochemical property by cyclic voltammetry (CV) test in oxygen saturated and deoxygenated 10-2 M phosphate solutions, respectively. According to the CV results, amperiometric response under the negatively applied potentials after -300 mV vs. Ag/AgCl would experience oxygen interference, while under potentials exceeding -300 mV no oxygen interference was observed. After evaluating various calibration curves, the amperometic signals under -250 mV validate a good linear response to different logarithm of phosphate concentrations with stable sensitivity and significant suppression of oxygen interference effects. [1] W. H. Lee, Y. Seo, and P. L. Bishop, "Characteristics of a cobalt-based phosphate microelectrode for in situ monitoring of phosphate and its biological application," Sens Actuators B Chem., vol. 137, pp. 121-128, 2009. [2] R. K. Meruva and M. E. Meyerhoff, "Mixed Potential Response Mechanism of Cobalt Electrodes toward Inorganic Phosphate," Anal. Chem., vol. 68, pp. 2022-2026, 1996. [3] T. Kidosaki, S. Takase, and Y. Shimizu, "Electrodeposited Cobalt-Iron Alloy Thin-Film for Potentiometric Hydrogen Phosphate-Ion Sensor," Journal of Sensor Technology, vol. 2, pp. 95-101, 2012. [4] A. J. Bard and L. R.Faulkner, ELECTROCHEMICAL METHODS: Fundamentals and Applications, 2 ed.: JOHN WILEY &SONS, INC., 2001. [5] P. E. Bradley and D. Landolt, "Pulse-plating of copper - cobalt alloys," Electrochimica Acta, vol. 45, pp. 1077-1087, 1999.

Anodic dissolution of magnetic layers based on cobalt and nickel in conditions of electrodeposition of multilayered nanostructures by a single-bath method

Methods of quartz microgravimetry (in solutions containing no copper ions) and stripping voltammetry (in copper-containing solutions) are used to study the process of anodic dissolution of thin deposits of pure Co and Ni and deposits of these metals with inclusion of copper in the potential region of copper deposition. It is shown that, under these conditions, Ni practically does not dissolve in either the sulfate or chloride-containing electrolytes, whereas Co dissolves in sulfate electrolytes at a rate that is dependent on the potential and increases with its shift into the positive region. Stability of ternary CoNiCu deposits is examined and it is demonstrated that additionally inserting Ni in the composition of a magnetic CoCu layer facilitates suppression of selective dissolution of Co.

Giant magnetoresistance and magnetism of heterogeneous CoCu produced by ion-beam techniques

Magnetic properties and giant magnetoresistance (GMR) of granular CoCu layers produced by ion-beam mixing were investigated. Laser-deposited CoCu multilayers with an integral composition of Co 20Cu 80 were ion-beam mixed with 150 keV Cu +. At a maximum fluence of 5×10 15 Cu/cm 2 the multilayer structure is completely replaced by a granular microstructure. Thermal magnetization curves indicate a broad distribution of Co-cluster sizes with superparamagnetic contributions. The magnetoresistance increases strongly by ion-beam mixing. There is evidence for strong magnetic interaction effects related with irradiation damages. The interaction effects can be reduced by annealing, which further increases the magnetoresistance.

X-RAY SMALL-ANGLE REFLECTION AND HIGH-ANGLE DIFFRACTION STUDIES ON Co/Cu MAGNETIC MULTILAYERS

With varying thickness of the spacer near the second oscillatory GMR peak in Co/Cu system, a series of glass/Fe/[ Co / Cu ]20/ Co multilayers are prepared by magnetronsputtering technique. The MR values are relatively small. High angle X-ray diffraction shows that the copper crystallizes in fcc structure with (111) texture and the cobalt crystallizes in hcp structure with (002) preferential orientation. There is a mixed amorphous CoCu layer at the interface due to the diffusion between cobalt and copper, which may decrease the MR value. The thickness, the mass density for each sub-layer and the surfacial and interfacial roughnesses are refined from the X-ray specular reflectivity measurement.