NiFe Layer Research Articles

Defective layered NiFe double hydroxides anchored on self-supported CoNi-nitrogen doped carbon nanotube composite as advanced electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is an essential process during electrochemical water-splitting. Due to its sluggish kinetics, low cost and highly efficient catalyst is invariably desired to decrease its overpotential for large-scale application. However, the overpotential of most advanced OER electrocatalysts is still more than 200 mV at the current density of 10 mA cm−2. In this work, we constructed active layered NiFe double hydroxides with cation defects on self-supported three-dimensional (3D) CoNi nitrogen-doped carbon nanotube composite substrate as integrated OER catalyst. Strikingly, electrochemical measurements showed that the optimized sample exhibited outstanding OER activity with low overpotentials of 178 and 268 mV at the current densities of 10 and 100 mA cm−2 in alkaline environment, alongside a good durability. The excellent OER performance was ascribed to the strongly synergistic effect of intrinsically active NiFe double hydroxide layers with abundant cation vacancies and 3D carbon nanotube composite substrate with good conductivity and various functional moieties, thus facilitating the electrocatalytic kinetic.

A 3D rGO-supported NiFe2O4 heterostructure from sacrificial polymer-assisted exfoliation of NiFe-LDH for efficient oxygen evolution reaction

NiFe2O4 takes an attractive potential candidate for oxygen evolution reaction (OER) catalysts, however, its usual preparation based on high-temperature calcination limits exposure of catalytically active sites. Herein, we report a new and efficient strategy for preparing NiFe2O4 supported by three-dimensional graphene network (NFO/3DGN) electrocatalysts. Specifically, NiFe layered double hydroxide (NiFe LDH) was exfoliated to single layer by polylactic acid (PLA), single layer NiFe LDH was released when PLA was hydrolyzed, and PLA hydrolysate etched single layer NiFe LDH to NiFe2O4; Meanwhile, the lamellar graphene oxide was reduced to 3DGN, so that NiFe2O4 was loaded on 3DGN, which means the agglomeration of NiFe2O4 could be prevented and efficient electron transmission channels for NiFe2O4 could be provided due to 3DGN. The as-prepared NFO/3DGN-10 exhibited an excellent electrocatalytic activity and stability for OER in an alkaline solution (with a low overpotential of 272 ± 25 mV at 10 mA cm−2 with a Tafel slope of 64 mV dec−1). Based on theoretical calculations, the reaction energy barrier of NiFe2O4 on the speed determination step reduced significantly owing to 3DGN. These results indicate that this facile fabrication method is a promising route for developing high-performance catalysts based on mixed metal spinel oxides supported by 3DGN.

Multilayered Cu/NiFe thin films for electromagnetic interference shielding at high frequency

Cu/NiFe multilayers with different structures were fabricated by electroplating for electromagnetic wave interference shielding in the high-frequency region. The electromagnetic wave interference shielding effectiveness of the symmetric, asymmetric, and thickness-gradient multilayer films was evaluated to optimize these structures. The thickness of the NiFe layer, which acts as an interlayer between Cu layers, is an important factor. The five-layered thin film (S9), with a thickness gradient that continues to increase toward the lower layer, shows an electromagnetic interference shielding effectiveness of − 74 dB in the wideband region, even though the total thickness of the multilayer is 1 µm. Focused ion beam, scanning electron microscopy, vector network, X-ray diffraction, four-point probe, and inductively coupled plasma–optical emission spectroscopy analyses were performed to characterize the multilayered Cu/NiFe thin films. • A Cu/NiFe multilayer was fabricated via electroplating. • The electrical conductivity and shielding effectiveness were investigated. • The electromagnetic interference shielding mechanism of the multilayer was studied.

Features of Galvanostatic Electrodeposition of NiFe Films with Composition Gradient: Influence of Substrate Characteristics

NiFe films with a composition gradient are of particular interest from the point of view of fundamental science and practical applications. Such gradient magnetic structures may exhibit unique functional properties useful for sensory applications and beyond. The issue surrounds the anomaly concerning the compositional gradient formed near the substrate in electrolytically deposited binary and ternary iron-containing alloys, which has not previously been clearly explained. In this work, light is shed on this issue, and a clear relationship is found between the structure and surface properties of the substrate, the initially formed NiFe layers and the film composition gradient.

Switching the sign of magnetic anisotropy field in YBCO/NiFe/IrMn heterostructure induced by superconducting transition

We studied the influence of the superconducting state on the magnetic properties in a thick IrMn(100 nm)/NiFe(100 nm) bilayer deposited by magnetron sputtering onto an yttrium–barium–copper–oxide (YBCO) substrate that was previously synthesized by the acetate method. The results from magnetization experiments showed that the sign of the effective exchange fields switched from positive, in the as-prepared heterostructure, to negative values when the sample goes below the superconducting temperature of the YBCO substrate. We, thus, demonstrated that the YBCO substrate, in its superconducting state, strongly influences the magnetic anisotropy of the thick ferromagnetic NiFe layer due to the proximity effect that occurs at the YBCO–NiFe interface, where a non-collinear magnetic spin structure is formed during the in-field sample deposition.

Deterministic magnetic moment rotation in antiferromagnetic material by piezoelectric strain modulation

Antiferromagnetic (AFM) spintronic devices play a vital role in the development of novel spintronic devices due to their attractive features. Herein, the interfacial state manipulation of the AFM IrMn material is investigated by combining a ferroelectric single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) with an electric field (E-field)-controlled magnetic moment arrangement of the IrMn film. A PMN-PT/Cu/IrMn/NiFe heterostructure is chosen to confirm the deterministic manipulation of AFM interfacial states and its angle of magnetic moment rotation. The appropriate thickness of the Cu layer is selected to disrupt the strain-mediated magnetoelectric coupling between the NiFe layer and PMN-PT substrate. The NiFe film reference layer can reflect the variation in AFM interfacial states via the exchange bias. When the E-field is applied, an in-plane piezoelectric strain is produced. If IrMn responds to the strain, its magnetic moment rotates from [001] to [1−10] depending on the crystal orientation of PMN-PT. Based on the experimental results and theoretical analyses, a rotation in the magnetic moment of the IrMn layer by ~20° is confirmed. This work provides convincing evidence for the manipulation of E-field-controlled AFM interfacial states and describes a reliable method for achieving the rotation angle of AFM moments, which can help to accelerate the development of AFM spintronic devices.

Theoretical approach and experimental investigation of spin current tunnelling in Ni80Fe20/Si3N4/Fe40Co37Zr11N12 magnetically collinear trilayer films with defined in-plane uniaxial anisotropy

Ferromagnetic trilayer film systems with nonferromagnetic Si3N4 interface layers were fabricated by using magnetron sputtering. A post-annealing process was carried out at 400 °C for 2 h in a static magnetic field, in order to induce an in-plane uniaxial anisotropy. The present study introduces the exchange interaction between ferromagnetic layers which influences the static magnetisation properties as well as the natural resonance frequency behaviour and its damping features, i.e., damping and anti-damping effects. This is expressed by the total damping parameter αitot = αGi ± αspi, which is enhanced or reduced by a spin transfer torque damping parameter ± αspi whereupon Gilbert bulk damping αGi is considered to be independent. The static polarisation loops are slightly but noticeably different, caused by an interface with thickness up to 100 nm, which reflects a decreasing exchange interaction. With varying the interface thickness, the films also show a distinct variation in their frequency spectra. This leads to the conclusion that spin currents caused by spin pumping arise, and tunnelling within a Si3N4 insulating barrier generates spin transfer torque. This can be assumed because the observed ferromagnetic resonance dual lines show remarkable changes in their Full Width at Half Maxima (FWHM) at frequencies of approximately 600 MHz caused by the Ni80Fe20 layers and 2.32 GHz caused by the Fe40Co37Zr11N12 layers. Regarding the FWHM of the resonance frequency spectra in association with the damping constant αeff on the dependence of the interface layer thickness, one can observe an exponential curve shape for both ferromagnetic layers, which is obviously a sign for the interaction between the layers through a spin current tunnelling mechanism.

Enhanced Nitrite Electrovalorization to Ammonia by a NiFe Layered Double Hydroxide

AbstractThe development of non‐precious metal (NPM) electrocatalysts for efficient nitrite‐to‐ammonia upcycling is key to enabling a sustainable society. Here, an earth‐abundant NiFe layered double hydroxide (LDH) is prepared to electrochemically reduce nitrite with a Faradaic efficiency as high as 85 %, an ammonia selectivity reaching 98 %, and an ammonia yield rate up to 351 μmol h−1 mgcat−1, rivaling the performance metrics of state‐of‐the‐art NPM catalysts. NiFe LDH further displays excellent stability after 10 consecutive electrolysis runs with its nanostructure unperturbed. By conducting electroreduction of nitrite in a range of solutions, the electrolyte identity is found to play an important role in dictating the overall nitrite removal activity. Through a comparative study with MgFe and NiAl inorganic solids, Ni and Fe are demonstrated to boost nitrite valorization rate as well as ammonia selectivity and yield in a synergistic manner. Taken together, these low‐cost catalysts provide a promising strategy for one‐step conversion of nitrite into ammonia exclusively with implications in next‐generation wastewater treatment and green industrial commodity production.

Enhanced low-frequency microwave absorption performance of FeNi alloy coated carbon foam assisted by SiO2 layer

The hierarchical structures of carbonized melamine foam modified by FeNi alloy and silicon layer (CMF/FeNi-SiO2) have been fabricated by a magnetron sputtering method. The as-prepared CMF/FeNi-SiO2 composites exhibited a three-dimensional porous structure, with the framework uniformly covered by a FeNi layer with several hundred nanometers and an ultrathin SiO2 layer, which demonstrated soft magnetic properties at room temperature. Moreover, the microwave absorption performance of the foam was investigated in the frequency range from 2 to 18 GHz. The results showed that the microwave absorption performance of CMF/FeNi-SiO2 composite was significantly enhanced in the low-frequency range compared with CMF/FeNi. The minimum reflection loss of CMF/FeNi-SiO2 with an absorption thickness of 4.1 mm was about −53 dB at 3.38 GHz and reached an effective absorption bandwidth of 0.93 GHz (from 2.93 GHz to 3.86 GHz). The frequency bandwidth of 8 GHz (2.35 ~ 6.35 GHz, 8.4 ~ 12.4 GHz) with absorption loss ≤ −10 dB and the frequency bandwidth of 2.05 GHz (2.62 ~ 4.67 GHz) with absorption loss ≤ -20 dB demonstrated the CMF/FeNi-SiO2 a high-efficient absorber in the low-frequency band (2–6 GHz), which stemmed from improved impedance matching and attenuation capacities.

Magnetization reversal properties and magnetostatic interactions of disk to rod-shaped FeNi layers separated by ultra-thin Cu layers

From fast magnetic memories with low-power consumption to recording media with high densities, realizing the magnetization reversal and interaction of magnetic layers would allow for manipulating the ultimate properties. Here, we use a pulsed electrochemical deposition technique in porous alumina templates (50 nm in pore diameter) to fabricate arrays of nanowires, consisting of FeNi layers (26−227 nm in thickness) with disk to rod-shaped morphologies separated by ultra-thin (3 nm) Cu layers. By acquiring hysteresis curves and first-order reversal curves (FORCs) of the multilayer nanowire arrays, we comprehensively investigate magnetization reversal properties and magnetostatic interactions of the layers at different field angles (0° ≤ θ ≤ 90°). These involve the extraction of several parameters, including hysteresis curve coercivity (H c Hyst ), FORC coercivity (H c FORC ), interaction field distribution width (ΔH u ), and irreversible fraction of magnetization (IF m ) as a function of θ. We find relatively constant and continuously decreasing trends of H c Hyst when 0° ≤ θ ≤ 45°, and 45° < θ ≤ 90°, respectively. Meanwhile, angular dependence of H c FORC and IF m shows continuously increasing and decreasing trends, irrespective of the FeNi layer morphology. Our FORC results indicate the magnetization reversal properties of the FeNi/Cu nanowires are accompanied with vortex domain wall and single vortex modes, especially at high field angles. The rod-shaped layers also induce maximum ΔH u during the reversal process, owing to enhancements in both magnetizing and demagnetizing-type magnetostatic interactions.

Thickness dependence of anomalous Hall and Nernst effects in Ni-Fe thin films

We systematically investigate the Ni-Fe layer thickness ($t$) dependence of the anomalous Hall effect (AHE) and anomalous Nernst effect (ANE). The AHE and ANE show different behavior in the $t$ dependence; the sign of the anomalous Hall resistivity changes around $t=9\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, whereas the anomalous Nernst coefficient (${S}_{\mathrm{ANE}}$) keeps almost constant regardless of $t$, namely, no sign change of ${S}_{\mathrm{ANE}}$ with $t$. We analyze ${S}_{\mathrm{ANE}}$ and separate it into the contribution coming from the transverse thermoelectric conductivity (${\ensuremath{\alpha}}_{xy}$) and the AHE contribution coming from the Seebeck effect. The detailed analysis for ${S}_{\mathrm{ANE}}$ concludes that the AHE contribution is negligibly small and ${\ensuremath{\alpha}}_{xy}$, which is related to the anomalous Hall conductivity (${\ensuremath{\sigma}}_{xy}$) via the Mott relation, is also independent of $t$. To gain insight into the difference in the $t$ dependence of ${\ensuremath{\sigma}}_{xy}$ and ${\ensuremath{\alpha}}_{xy}$, we clarify the origin of sign reversal in the AHE. The sign reversal in the AHE is attributed to the competing contribution of the different sources of the AHE: the extrinsic and intrinsic mechanisms. The present experimental finding of the difference between the $t$ dependence on ${\ensuremath{\sigma}}_{xy}$ and ${\ensuremath{\alpha}}_{xy}$ suggests that the relative degree between the extrinsic and intrinsic processes for the AHE is quite different from that for the ANE in the case of Ni-Fe.

Electroplated Ni-Fe Layer on Stainless Steel Fiber Felt as an Efficient Electrode for Oxygen Evolution Reaction

Electroplated Ni-Fe Layer on Stainless Steel Fiber Felt as an Efficient Electrode for Oxygen Evolution Reaction

Giant efficiency for charge-to-spin conversion via the electron gas at the LaTiO3+δ/SrTiO3 interface

Spin-to-charge interconversion has been extensively investigated to improve its efficiency of charge-to-spin conversion, realizing magnetic switching by the technique of low-power spin-orbit torque (SOT). The quasi-two-dimensional electron gas (q2DEG) formed at the interface between insulating ${\mathrm{SrTiO}}_{3}$ (STO) and ${\mathrm{LaTiO}}_{3+\ensuremath{\delta}}$ (LTO) is supposed to possess strong Rashba spin-orbit coupling. Here, we show that a charge current flowing along the LTO/STO interface, which hosts a q2DEG, can efficiently generate a spin current, producing a strong SOT on adjacent NiFe layer as confirmed by spin-torque ferromagnetic resonance. The maximal charge-to-spin conversion efficiency is as large as $\ensuremath{\sim}2.4$ at room temperature, appearing in the NiFe/LTO/STO structure with a LTO thickness of 4 nm. This efficiency is much larger than that of heavy meals. With the decrease of temperature, the conversion efficiency only exhibits a slight decrease, remaining $\ensuremath{\sim}1.5$ at 20 K. The present work reveals the great potential of conducting oxide interface for oxide-based spintronics.

Picosecond time-resolved X-ray ferromagnetic resonance measurements at Shanghai synchrotron radiation facility

An experimental picosecond time-resolved X-ray ferromagnetic resonance (TR-XFMR) apparatus with a time resolution of 13 ps (RMS) or 31 ps (FWHM) was constructed and demonstrated in the 07U and 08U1A soft X-ray beamlines at the Shanghai Synchrotron Radiation Facility (SSRF) using pump-probe detection and X-ray magnetic circular dichroism (XMCD) spectroscopy. Element and time-resolved ferromagnetic resonance was excited by continuous microwave phase-locking of the bunch clock within the photon beam during synchrotron radiation and was characterized by detecting the magnetic circular dichroism signals of the elements of interest in the magnetic films. Using this equipment, we measured the amplitude of the element-specific moment precession during ferromagnetic resonance (FMR) at 2 GHz in a single Ni81Fe19 layer.

Sulfur Engineering on NiFe Layered Double Hydroxide at Ambient Temperature for High Current Density Oxygen Evolution Reaction

Sulfur Engineering on NiFe Layered Double Hydroxide at Ambient Temperature for High Current Density Oxygen Evolution Reaction

Metal-Organic Framework-Derived Hollow CoSx Nanoarray Coupled with NiFe Layered Double Hydroxides as Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

For effective hydrogen production by water splitting, it is essential to develop earth-abundant, highly efficient, and durable electrocatalysts. Herein, the authors report a bifunctional electrocatalyst composed of hollow CoSx and Ni-Fe based layered double hydroxide (NiFe LDH) nanosheets for efficient overall water splitting (OWS). The optimized heterostructure is obtained by the electrodeposition of NiFe LDH nanosheets on metal-organic framework-derived hollow CoSx nanoarrays, which are supported on nickel foam (H-CoSx @NiFe LDH/NF). The unique structure of the hybrid material not only provides ample active sites, but also facilitates electrolyte penetration and gas release during the reactions. Additionally, the strong coupling and synergy between the hydrogen evolution reaction (HER) active CoSx and the oxygen evolution reaction (OER) active NiFe LDH gives rise to the excellent bifunctional properties. Consequently, H-CoSx @NiFe LDH/NF exhibits remarkable HER and OER activities with overpotentials of 95 and 250 mV, respectively at 10 mA cm-2 in 1.0 M KOH. Even at 1.0 A cm-2 , the electrode requires small overpotentials of 375 mV (for HER) and 418 mV (for OER), respectively. An electrolyzer based on H-CoSx @NiFe LDH/NF demonstrates a low cell voltage of 1.98 V at a current density of 300 mA cm-2 and good durability for 100 h in OWS application.

Deformation Structure Around a Crack in γ′-Fe4N Layer of Nitrided Extra-Low-Carbon Steel Subjected to Cyclic Tensile Test

Deformation Structure Around a Crack in γ′-Fe4N Layer of Nitrided Extra-Low-Carbon Steel Subjected to Cyclic Tensile Test

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.

Spin Reorientation Transition and Exchange Bias in Hard/Soft Tb–Co/FeNi Films

Magnetization studies were carried out for Tb–Co thin films and Tb–Co/FeNi bilayers, prepared by magnetron sputtering technique. The composition of the Tb–Co films varied in the range of 19–24 at.%. All Tb–Co films were found to have perpendicular magnetic anisotropy in a wide temperature range. In addition, for some Tb–Co films, a spin reorientation transition was observed in the investigated temperature range. An analysis of the obtained results suggests that, in the course of deposition of the FeNi layer onto the Tb–Co layer, an interlayer magnetic boundary is formed, and its parameters depend on the composition of the Tb–Co layer. The magnetic structure peculiarities of this boundary determine the value of the exchange bias in Tb–Co/FeNi bilayers and its temperature dependence.

Manipulation of Magnetic Properties and Magnetoresistance in Co/Cu/γ′-Fe4N/Mica Flexible Spin Valves via External Mechanical Strains

The strain-tailored magnetic and electronic transport properties in flexible spin valves (SPVs) have attracted attention due to their practical applications in flexible spintronic devices. Here, magnetic and spin-dependent electronic transport properties of Co/Cu/γ′-Fe4N/mica flexible SPVs are investigated. The strain-induced change ratio of magnetoresistance (MR) is 49% in Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(11.0 nm) flexible SPVs. The magnetic properties of Co(4.8 nm)/Cu(7.5 nm)/γ′-Fe4N(7.9 nm) flexible SPVs show mechanical stability at bending strains. The magnetic properties of flexible SPVs did not deteriorate after 100 times of bending and 60 h of bending. As the Co layer thickness decreases from 7.2 to 2.4 nm, the sign of MR changes from negative to positive. A negative MR appears due to the opposite scattering spin asymmetry coefficients between Co/Cu and γ′-Fe4N/Cu interfaces. A positive MR arises from the same scattering spin asymmetry coefficients at Co/Cu and γ′-Fe4N/Cu interfaces or magnetization misalignments between Co and γ′-Fe4N layers. Additionally, the MR is a combination of an anisotropy magnetoresistance and a giant magnetoresistance effect, which has been confirmed by MR–H curves with different measurement configurations (Hin-plane∥I, Hin-plane⊥I and Hout-of-plane⊥I) and M–H curves. The M–H curves show that the magnetization of γ′-Fe4N reverses before that of the Co layer.