NiFe Deposition Research Articles

Electrodeposited Ni-Fe-TiO2 Alloy Composites As a Bifunctional Electrocatalyst for Alkaline Water Splitting Reactions

The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) that governs electrolytic water splitting are of interest as a way to store energy from renewable sources. However, replacing noble metal electrocatalyst with those comprised of lower cost, earth abundant elements remains a challenge as these materials impart a higher overpotential, and hence energy requirement, to both reactions. Guided by the recognized enhanced activity of Ni-based hydroxides in alkaline media,1 and known enhancements of TiO2 in Co-Mo alloys for HER, the examination of Ni-Fe-TiO2 alloy composite electrocatalysts are explored.2 Nano-scale TiO2 particles were embedded into Ni-Fe alloys by using galvanic and pulse-reverse electrodeposition, onto rotating cylinder electrodes. Pulse-reverse electrodeposition considerably increased the concentration of the particles incorporated into the alloy. The composition and morphology was characterized by x-ray fluorescence (XRF) spectroscopy and scanning electron microscopy (SEM), respectively. The addition of particles to the electrolyte affected both the deposit composition and morphology. The alloy composites were then used as electrocatalysts in 1 M KOH to characterize HER and OER via linear sweep voltammetry on the resulting hydroxide surface. The surface area was examined in a ferri/ferrocyanide electrolyte. The polarization data in 1 M KOH shows a significant reduction in the HER overpotential when TiO2 particles are present in the Ni-Fe deposit. The surface analysis of Ni-Fe and Ni-Fe-TiO2 confirmed that the improvement in HER activity is not due to surface roughness but an intrinsic one. The OER rate was not significantly altered by the included TiO2 particles in the deposit. Stability of the electrocatalysts under an electrolysis for HER and an independent electrolysis for OER was examined. References M. I. Jamesh. J. Power Sources 333, 213 (2016); A. Eftekhari. Int. J. Hydrog. Energy 42, 11053 (2017); J. Zhao, J-J. Zhang, Z-Y Li, X-H Bu, Small, 16 2003916 (2020).C. Wang, H. K. Bilan, and E. J. Podlaha. J. Electrochem. Soc. 166 F661 (2019). C. Wang and E. J. Podlaha, J. Electrochem. Soc. 167, 132502 (1~4) (2020).

(Invited) Graphene Oxide As an Additive for Ni-Fe Electrodeposition

In contrast to graphene, graphene oxide (GO) is readily disperse in aqueous electrolytes and can be reduced along with nickel and iron metal ions. While others had incorporated graphene in Ni-Fe deposits, no previous studies have addressed the role of GO particles on metal deposition. Ni-Fe is characterized by the anomalous codeposition behavior where there is a tendency of more Fe to be deposited than Ni even though there is an excess of Ni ions in the electrolyte. This behavior has been modeled assuming adsorbed intermediates. Here, the influence of GO on the deposit composition, structure and anomalous codeposition effect is investigated. The deposits were galvanostatically electrodeposited from a boric acid-sulfamate electrolyte at pH 2 containing commercial graphene oxide platelets. Two different cell configurations were examined:1) a rotating cylinder electrode (RCE) and 2) a copper mesh. The rotating cylinder as a working electrode was used in order to investigate mass transport. The copper mesh working electrode was placed in close contact to a flat bottom pH probe in order to examine the local pH change. The addition of GO to the electrolyte had an effect on the deposit composition and the local pH change (Fig 1). The deposit composition had either more Ni or remained the same compared to an electrolyte without GO on the RCE electrode at electrode rotation rates of 372 and 1000 rpm (Fig 1 (a) and (b)). The larger Ni content in the deposit was due to an enhanced Ni partial current density in the presence of GO. The local pH during the deposition on the mesh electrode with vigorous electrolyte stirring increased the local pH (Fig 1(c)). The composition behavior is similar to the results from the RCEs, with higher Ni content in the presence of GO. The local pH increase when GO was present is considered a factor that drives the enhanced Ni content, that may be a consequence of changes in adsorbed hydrogen. GO was not incorporated into the deposit; however, it had a dramatic effect on the morphology. There was less micro-cracks when GO was present in the electrolyte suggesting less adsorbed hydrogen. Thus, GO influenced the adsorbed intermediates making the electrodeposition less anomalous and having less cracks. Acknowledgement: This work was supported in part by the AESF Foundation. Figure 1. The influence of GO in the electrolyte during Ni-Fe electrodeposition (a) composition on a RCE, rotating rate (a) 372, (b)1000 rpm and (c) local pH measurements on a mesh electrode under vigorous stirring, 30 mA/cm2. Figure 1

Electrodeposited Ni-Fe-TiO2 Alloy Composites for the Hydrogen Evolution Reaction

Hydrogen is a carbon-free alternative energy source that is environmentally friendly, has high energy density, and is a promising fuel for future generations. Water splitting is an efficient way to produce hydrogen, requiring a catalyst with a small overpotential and Tafel slope, and good stability. However, only 4 % of global hydrogen is produced by water electrolysis due to high cost and lack of inexpensive replacements of the active platinum electrocatalyst.1 However, replacing these noble metal electrocatalysts with those comprised of lower, earth-abundant elements remains challenging as these materials impart a higher overpotential and thus require higher energy. Guided by the recognised enhancements of TiO2 particles in Co-Mo alloys for HER, earth-abundant, low-cost Ni and Fe metals are examined as composite electrocatalysts Ni-Fe-TiO2 towards HER.2 Nano-scale TiO2 particles were embedded into Ni-Fe alloys by using galvanic and pulse-reverse electrodeposition, onto rotating cylinder electrodes. Pulse-reverse electrodeposition considerably increased the concentration of the particles incorporated into the alloy. The composition and morphology were characterized by X-ray fluorescence (XRF) spectroscopy and scanning electron microscopy (SEM), respectively. The addition of particles to the electrolyte affected both the deposit composition and morphology. The alloy composites were then used as electrocatalysts in 1 M KOH to characterize HER via linear sweep voltammetry on the resulting hydroxide surface. The surface area was examined in a ferri/ferrocyanide electrolyte. The polarization data in 1 M KOH shows a significant reduction in the HER overpotential when TiO2 particles are present in the Ni-Fe deposit. The surface analysis of Ni-Fe and Ni-Fe-TiO2 confirmed that the improvement in HER activity is not due to surface roughness but an intrinsic one. The stability of the electrocatalysts under an electrolysis for HER was examined at -10 mA/cm2 for 24 hr and the working electrode potential remained stable over time; Tafel polarization curves after electrolysis were similar to those prior to electrolysis. References Le, P. A., Trung, V. D., Nguyen, P. L., Phung, T. V. B., Natsuki, J., & Natsuki, T. RSC advances, 13(40), 28262-28287 (2023).C. Wang, H. K. Bilan, and E. J. Podlaha. J. Electrochem. Soc. 166 F661 (2019). C. Wang and E. J. Podlaha, J. Electrochem. Soc. 167, 132502 (1~4) (2020).

An asymmetric electrode matching reversible kinetics of oxygen reaction for a rechargeable Zn-air battery

The development of zinc-air batteries (ZABs) is hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) which occur in the complex interfaces between gaseous oxygen, liquid electrolyte and solid catalyst. Designing a rational interface that aligns with the kinetics of these multi-phase reactions is of utmost importance. Herein, an asymmetric cathode (Asy-electrode) has been designed and fabricated that the carbon nanotubes arrays (CNAs) encapsulating Co nanoparticles grown on carbon cloth is used as the aerophilic side (AI-side) to match and catalyze the ORR kinetics, the other side that deposition of NiFe layered double hydroxide (NiFe-LDH) on the CNAs plays as aerophobic side (AO-side) to accelerate the OER kinetics. The Asy-electrode effectively balances the adsorption and desorption of O2 and OH–, and promotes the efficient transport of gaseous and liquid reactants and products. Therefore, the efficiency of ORR and OER onto the corresponding catalytic sites of Co/CNAs and NiFe-LDH/CNAs are significantly enhanced. Consequently, the ZAB employing the asymmetric cathode can acquire a remarkable higher power density (236.26 mW cm−2) and an excellent long-term cycling stability (over 1920 cycles at 10 mA cm−2) due to the enhanced kinetic and the improved reversibility of the charge–discharge reaction on the cathode benefiting from the aerophilic/hydrophilic interfacial construction on each side of electrode. The present study could explore a route to design the catalysts from the view of matching the multi-phase reaction characteristics.

Electrodeposition of Ni-Fe-Co and Ni-Fe Graphene Oxide Alloy Composites

Graphene platelets can impart unique properties to metal matrices, such as enhanced conductivity, mechanical, thermal properties and catalytic activity.1,2 The electrodeposited process to fabricate composite metal matrices has an advantage over other techniques because it can avoid high heat treatment and deformation during fabrication, which can damage the intrinsic structure of graphene plates. Graphene itself is difficult to disperse and incorporate into electrodeposited films, but the oxidized form, having abundant surface functional groups, can be readily dispersed into aqueous solutions. Examples of electrodeposited metals with included graphene oxide (GO) from the electrolyte include elemental deposits such as Ni,3-4 Cu,2,5-6 and Co.7,8 In these studies, graphene oxide addition to the metal matrices promoted enhanced thermal conductivity in Cu,6 grain refinement in Ni4 and Cu5, improved wear resistance of Co7,8 and in the case of Ni changed its preferred crystallographic orientation.3 In alloy electrodeposition, the particle in the electrolyte may also alter the deposit composition through disparate changes in the individual metal ion partial current densities. The alloys containing Fe, Ni and Co from the reduction of their metal ions are of interest for their peculiar behavior, where there tends to be an inhibition of the more noble species reduction reaction (e.g. Ni, Co) in favor of the less noble (Fe) referred to as anomalous codeposition.9 To examine the influence of graphene oxide on the deposit composition, Ni-Fe-Co alloys were galvanostatically electrodeposited from a boric acid-sulfamate electrolyte containing commercial graphene oxide plates. Rotating disk electrodes were used to control the hydrodynamic environment near the cathode. The composition, morphology and structure were examined. The addition of graphene oxide resulted in a change in deposit composition, particularly for Fe and Ni, at low cathodic current densities less than 50 mA/cm2, with the deposit becoming less anomalous with the addition of graphene oxide. The change in composition is thought to be derived from a decrease in adsorbed iron intermediates from an anomalous codeposition model. The partial current densities of Ni-Fe-Co deposition with a measure of ohmically corrected potential are compared with Ni-Fe, Ni and Fe deposition with graphene. References H.G. P. Kumar, M. A.Xavior, Procedia Eng. 97 1033 (2014).J. Biswal, P. R. Vundavilli, and A. Gupt, J. Electrochem. Soc., 167 146501 (2020).D. Kuang, L. Xu, L. Liu, W. Hu, Y. Wu, Appl. Surf. Sci., 273, 484 (2013).J. Li, Z. An, Z. Wang, M. Toda, and T. Ono, ACS Appl. Mater. Interfaces, 8, 3969 (2016). L. P. Pavithra, B. V. Sarada, K. V. Rajulapati, T, N. Rao and G. Sundararajan, Nature Sci Rep 4, 4049 (2014).K. Jagannadham, Metall. Mater. Trans B 43 B 316 (2012).C. Liu, F. Su, J. Liang, Appl. Surf. Sci. 351 889 (2015).A. Toosinezhad, M. Alinezhadfar, S. Mahdavi, Ceram. Int., 46, 16886 (2020).A. Brenner, Electrodeposition of Alloys: Principles and Practice, Academic Press Inc., New York, pp. 399-450 (1963).

Large amplification of the sensitivity of symmetric-response magnetic tunnel junctions with a high gain flux concentrator

Miniaturized, ultra-sensitive and easily integrable magnetometers are needed for many applications like space exploration or medical survey. In this study, we combine innovative magnetic tunnel junctions having a symmetric resistance-field (R–H) response with a high gain flux concentrator. In our junctions, the magnetization of the free layer (FL) is stabilized in an anti-parallel configuration with respect to that of the reference layer. This configuration is achieved by using a soft exchange pinning of the FL. We precisely adjust the exchange field value with a dusting layer of ruthenium used to weakly decouple the magnetization of the FL from the local moments of the antiferromagnet. In order to improve the junction's sensitivity, we study the influence of the exchange field value and of the shape anisotropy on the even-function R–H response. In particular, we compare circular junctions with elliptic or rectangular junctions of various aspect ratios and orientations. We find that the sensitivity of the junctions increases when reducing the soft-pinning exchange field and by using junctions with an elongated shape in the direction of the applied field. Finally, we were able to further increase the sensitivity by a factor 440 due to a flux concentrator placed around the junction by electrochemical deposition of NiFe. Its design is optimized (elongated shape, 5–7 μm thickness and 10 μm air-gap) in order to obtain this very high gain. The complete sensor system composed of these magnetic tunnel junctions and the flux concentrator allows to reach sensitivities larger than 1000%/mT.

Evaluation of electrosynthesized reduced graphene oxide-Ni/Fe/Co-based (oxy)hydroxide catalysts towards the oxygen evolution reaction.

In this work, the specific role of the addition of graphene oxide (GO) to state-of-the-art nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxides/hydroxides towards the oxygen evolution reaction (OER) is investigated. Morphology, structure, and OER catalytic activity of the catalysts with and without GO were studied. The catalysts were fabricated via a two-step electrodeposition. The first step included the deposition of GO flakes, which, in the second step, were reduced during the simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO were fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. A different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone. However, it was reduced in comparison to CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies showed that each of the catalysts specifically influenced the process. The improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.

Template-assisted synthesis of ultrathin graphene aerogels as bifunctional oxygen electrocatalysts for water splitting and alkaline/neutral zinc-air batteries

Low-cost, high-performance oxygen catalysts are critical for electrochemical water splitting and metal-air batteries. Herein, carbon aerogels with skeletons consisting of few-layer graphene are derived pyrolytically from a hydrogel precursor using an array of NaCl crystals as the template, exhibiting a high electrical conductivity (869 S m−1) and an ultralow mass density (11.1 mg cm−3). The deposition of NiFe layered double hydroxide (NiFe-LDH) nanocolloids renders the aerogels active towards both the oxygen reduction/evolution reactions (ORR/OER), with the performances highly comparable to those of commercial benchmarks in both alkaline and neutral media. Results from operando Raman spectroscopy measurements and first principles caculations suggest that Fe(OH)3 colloids facilitate the oxidation of Ni2+, which lowers the energy barrier to 0.42 eV for OER, whereas the nitrogen-doped carbon aerogels are responsible for the ORR activity. With the composites used as bifunctional oxygen catalysts for electrochemical water splitting and rechargeable zinc-air batteries, the performances in both alkaline and neutral media are markedly better than those based on the mixture of commercial Pt/C and RuO2. Results from this study highlight the unique advantages of ultrathin graphene aerogels in the development of effective catalysts for electrochemical energy devices.

Stripe domains in electrodeposited Ni90Fe10 thin films

Here we have investigated the formation of stripe domains in electrodeposited Ni90Fe10 films, a metallic alloy with relevant magnetoelastic properties. The X-ray diffractometry patterns confirm the deposition of NiFe with an experimental lattice parameter close to the theoretical value. We have analyzed the influence of both magnetic stirring and an applied magnetic field perpendicular to the sample plane on the formation of stripe domains in Ni90Fe10 films. It is observed the characteristic fingerprint of stripe domains, i.e. the transcritical shape in the in-plane hysteresis loops when the electrolyte is not magnetically stirred during electrodeposition. The quality factor reveals a moderate perpendicular magnetic anisotropy which is confirmed by the stripe periodicity inferred by Magnetic Force Microscopy. In particular, stripe domains are only visible by this technique when the sample thickness is well above the theoretical critical thickness for the stripe domains to be formed. Finally, in samples released after being grown in outward bent flexible substrates it has been promoted an induced in-plane magnetoelastic magnetic anisotropy that reduces the perpendicular magnetic anisotropy. The high quality of the samples studied in this work from the magnetoelastic point of view is reflected by the magnetostriction constant of −22 ppm that it has been experimentally inferred.

Periodic ultrasound-assisted electrodeposition of Fe–Ni alloy foil

Periodic ultrasound was introduced into the electroforming process to electrodeposit Fe–Ni foil layers with high properties and low coefficient of thermal expansion that satisfied the requirements for avionics packaging. Electrochemical analysis and morphological testing indicated that periodic ultrasound can sufficiently weaken the stripping effect caused by continuous high-power ultrasonic treatment. Under periodic ultrasonic treatment, applying both high current density and high ultrasonic power in the electroforming system is possible. By adjusting the current density and the duty cycle, Fe–Ni deposits with coefficients of thermal expansion (CTEs) ranging from 2.96 to 6.71 × 10−6/ °C were obtained. Compared to Fe–Ni alloys prepared via traditional electrodeposition methods, the Fe–Ni layers obtained in this study exhibit a larger range of CTE values and great improvements in other physical and mechanical properties. The Fe–Ni alloy foil obtained at a duty cycle of 0.57 and current density of 1 A/dm2 possessed a low surface roughness of 0.95 μm, the iron content of 63 wt.%, micro-hardness of 373.1 HV, Young's modulus of 133.7 MPa, and CTE of 5.39 × 10−6/ °C.

Studying structural, magnetic and morphological features of electrochemically fabricated thin films of Co–Ni–Fe with different Fe compositions

In this work, a detailed study on the influence of the Fe composition on the crystallite size, lattice parameter, crystallographic texture, coercive field (Hc), magnetic squareness ratio (SQR), domain structure, surface roughness and grain size in electroplated Co–Ni–Fe deposits was carried out. For this aim, Co–Ni67, Co–Ni61–Fe6 and Co–Ni54–Fe13 thin films with different Fe compositions were fabricated using electrochemical deposition technique. The results showed that the composition of Fe in the deposit depends on the concentration of Fe ions in the electroplating solution. An increase in the Fe composition caused a noticeable reduction in the size of crystallites and induced a considerable enhancement in the strength of the preferred orientation being in the [111] direction. It was also observed that an increase in the Fe composition makes the lattice parameter larger. Compared to other deposits, the Co–Ni54–Fe13 with the highest Fe composition exhibited a lower surface roughness and a more compact nodular surface topography consisting of relatively finer grains. All deposits displayed a stripe domain (SD) structure, an in–plane magnetic hysteresis loop with a vertical magnetization component and a semi–hard magnetic property. However, the Hc value, SQR parameter and SD width varied in accordance with the Fe composition.

The activation-free electroless deposition of NiFe over carbon cloth as a self-standing flexible electrode towards overall water splitting

The electroless deposition of NiFe over carbon cloth as a flexible electrode for overall water splitting was demonstrated.

Electroless Deposition of Ni-Fe Alloys on Scaffolds for 3D Nanomagnetism.

3D magnetic nanostructures are of great interest due to the possibility to design novel properties and the benefits for both technological applications such as high-density data storage, as well as more fundamental studies. One of the main challenges facing the realization of these three-dimensional systems is their fabrication, which includes the deposition of magnetic materials on 3D surfaces. In this work, the electroless deposition of Ni-Fe on a 3D-printed, non-conductive microstructure is presented. The deposited films exhibit low coercivity, with the saturation magnetization and composition corresponding to the archetypal soft magnetic material permalloy. For fundamental studies of 3D micromagnetism, this new development in fabrication offers the possibility to combine the flexibility of 3D nanofabrication techniques such as two-photon lithography for the fabrication of 3D scaffolds with a homogeneous soft ferromagnetic thin film, and thus represents an important step toward exploring the rich physics of complex 3D magnetic architectures with tailored properties and the development of advanced applications.

Normal Electrochemical Deposition NiFe

Due to heating of the electrolyte is an excluded abnormal codeposition alloy components and reduced variation of process parameters to achieve optimal magnetic properties Ni81Fe19 films of magnetic field concentrators. Proposed chloride electrolyte pH adjusted with hydrochloric acid, which provides congruent electrochemical deposition of permalloy at heating and stirring. Magnetic properties of permalloy films are very sensitive to the variation of component relationships of 4.26. Control of accuracy of preparation of chloride electrolyte for electrochemical deposition of NiFe conducted using spectrophotometry. It is shown that the selection process of cooking the electrolyte for electrodeposition of Ni81Fe19 alloy and temperature allow to get normal, congruent electrochemical deposition of permalloy films. It has been established that the anomalous character of permalloy deposition associated with the main feature of iron ions-the existence of variable Valence iron with two or three values in the charge of ions during the hydrolysis of iron salts.

Normal Electrochemical Deposition NiFe

Due to heating of the electrolyte is an excluded abnormal codeposition alloy components and reduced variation of process parameters to achieve optimal magnetic properties Ni81Fe19 films of magnetic field concentrators. Proposed chloride electrolyte pH adjusted with hydrochloric acid, which provides congruent electrochemical deposition of permalloy at heating and stirring. Magnetic properties of permalloy films are very sensitive to the variation of component relationships of 4.26. Control of accuracy of preparation of chloride electrolyte for electrochemical deposition of NiFe conducted using spectrophotometry. It is shown that the selection process of cooking the electrolyte for electrodeposition of Ni81Fe19 alloy and temperature allow to get normal, congruent electrochemical deposition of permalloy films. It has been established that the anomalous character of permalloy deposition associated with the main feature of iron ions-the existence of variable Valence iron with two or three values in the charge of ions during the hydrolysis of iron salts.

Ultrasmall NiFe layered double hydroxide strongly coupled on atomically dispersed FeCo-NC nanoflowers as efficient bifunctional catalyst for rechargeable Zn-air battery

An atomically dispersed FeCo-NC material with the 3D flower-like morphology was used as a unique substrate for the controllable deposition of ultrasmall NiFe layered double hydroxide nanodots (termed as NiFe-NDs) to simultaneously promote the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The size-limiting growth of NiFe-NDs (~4.0 nm in diameter) was realized via the confinement of the 3D flower-like mesoporous structure and the rich N/O functionality of FeCo-NC. Benefiting from the distinctive structure with the simultaneously maximum exposure of both OER and ORR active sites, the NiFe-ND/FeCo-NC composite showed an ORR halfwave potential of 0.85 V and an OER potential of 1.66 V in 0.1 mol L KOH at 10.0 mA cm. In-situ Raman analysis suggested the activity of OER was derived from the Ni sites on NiFe-ND/FeCo-NC. Moreover, the NiFe-ND/FeCo-NC-assembled Zn-air battery (ZAB) exhibited a very small discharge- charge voltage gap of 0.87 V at 20 mA cm and robust cycling stability. Furthermore, the NiFe-ND/FeCo-NC composite was also applicable for fabricating all-solid-state ZAB to power wearable electronics with superior cycling stability under deformation. Our work could enlighten a new applicable branch of atomically dispersed metal-nitrogen-carbon materials as unique substrates for fabricating multifunctional electrocatalysts.

Characterisation of electroplated Ni45Fe55 thin films on n-Si (111)

ABSTRACTElectrodeposition of NiFe films, on hydrogen-terminated n-Si (111)-H from acidic dilute sulphate solution, was studied by electrochemical measurements at room temperature in the presence and absence of saccharin. The electroplating process kinetics was investigated by voltammetric study and the effect of Fe2+ concentration on the deposit composition was studied as well with energy dispersive spectrometry analysis. The average composition of the Ni45Fe55 film was obtained for Fe2+ concentration in the range of [0.030–0.035] mol L−1 at a current density of −6 mA cm−2. Correlation between Fe2+ concentration in the NiFe deposit and electronic properties was examined by electrochemical impedance spectroscopy. Film roughness depends on Fe2+ concentration and a smoother deposit was obtained for the Ni45Fe55 film. Very low coercivity (less than 1.3 Oe) was measured in the Ni45Fe55 film with a nominal thickness of 640 nm. The very soft magnetic properties of the NiFe films provide information about the low level of inhomogeneities present in these films.

Effects of Current Pulsation on Magnetic Properties and Giant Magnetoimpedance of Electrodeposited NiFe Coatings on Cu Wires

This work presents a systematic study of the effects of current pulsation on soft magnetic properties and giant magnetoimpedance (GMI) of nickel-iron (NiFe) coatings electrodeposited on copper wires. The specimens were prepared by the electrodeposition technique with controlled bath compositions and varied applied current waveforms. The microstructural and chemical investigations indicate that current pulsation with 50% duty cycle and 50 Hz frequency provides significantly smoother coating surface of uniform nodules, with comparable Fe content but different phase composition, as compared to the direct current condition. The vibrating sample magnetometer evidently shows that the deposits prepared with a pulsed current exhibit relatively small coercivity, below 4 Oe. Using the four-point probe technique, the MI ratio of the pulse deposits is found to reach a significantly high value above 2,000% with decent sensitivity. The benefits of current pulsation in improving the characteristics of NiFe deposits, and correspondingly the alloys’ soft magnetic properties and MI effects are demonstrated.

Stable room temperature magnetocurrent in electrodeposited permeable n-type metal base transistor

We investigated a permeable metal base transistor consisting of a ZnO/NiFe/Si heterostructure. Both ZnO and NiFe layers were grown by electrodeposition techniques, using only adhesive tape masks to define deposition regions. The base permeability can thus be controlled by varying the NiFe deposition time. We report here our best results obtained for the permeable NiFe base close to the electrical percolation threshold, which gives reasonable sensitivity to the device. Magnetocurrent measurements carried out at room temperature show that this permeable metal base transistor is stable and sensitive under applied magnetic fields of low intensities, ∼100 Oe, required for electronics integration.

Deposition of NiFe(200) and NiFe(111) textured films onto Si/SiO2 substrates by DC magnetron sputtering

The effect of substrate temperature T sub and bias voltage U bias on the texture of NiFe films with thickness d ∼ 30–340 nm deposited by DC magnetron sputtering onto Si(111)/SiO2 substrates under working gas pressure ∼ 0.2 Pa has been investigated. It has been demonstrated that films grown at room substrate temperature have the (111) texture that is refined under a negative bias voltage. The deposition of films onto a grounded (U bias ∼ 0) substrate heated to T sub ∼ 440–640 K results in the formation of textured NiFe(200) films.