NiFe Layer Research Articles

The role of boron on exchange coupling in NiFe/Ru1−xBx/FeCo trilayer structures

In this work, we study the interlayer exchange coupling, J, between two NiFe and FeCo layers in a series of NiFe/Ru1−xBx(d)/FeCo synthetic antiferromagnet (SAF) samples, where the thickness of the spacer layer, d, is varied from 0.4 nm to 0.9 nm, and the boron concentration, x, is varied from 0 to 15 at. %. The samples are studied as deposited and after being annealed at 250°C. B is deposited into the Ru spacer layer to investigate what occurs after annealing a FeCoB/Ru/FeCoB SAF structure, which is commonly used in modern nanoscale magnetic devices, in which the FeCoB layer crystallizes to FeCo and B diffuses to adjacent layers. We find that J in as-deposited samples is relatively unaffected by adding up to 15% B into the Ru spacer layer. However, after annealing at 250°C, J changes the sign from antiferromagnetic coupling to ferromagnetic coupling for spacer layers thinner than 0.45nm for 5% and 10% B and thinner than 0.525nm for 15% B. We used transmission electron microscopy energy-dispersive x-ray spectroscopy in order to investigate the diffusion of atoms within a similar Ta(2.5nm)/NiFe(0.8nm)/Ru1−xBx(23 nm) layer structure. We find that after annealing at 250°C, the sample containing 15% B within the Ru85B15 layer had significantly more diffusion of Fe into the Ru85B15 layer, from the NiFe layer, as compared to the sample with 0% B. Thus, the presence of B within the spacer layer enhances diffusion of Fe into the spacer layer.

The Effect of a Substrate Material on Composition Gradients of Fe-Ni Films obtained by Electrodeposition

The electrodeposition of FeNi alloy films was performed galvanostatically in the sulfate solution (Fe2+/Ni2+ mass ratio 1:2) in order investigate their co-deposition mechanism. The FeNi layers were deposited at variable substrates (copper, brass, silver) under the same chemical (electrolyte composition) and electric plating (current density value) conditions. After applying various time, substrates and external magnetic field orientation, the quality of the obtained film was examined. The surface morphology and crystallographic texture variation were investigated by the Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Wavelength Dispersive X-ray Fluorescence (WDXRF) and Laser Confocal Scanning Microscope (LCSM). The anomalous co-deposition of iron group metals is evidently dependent on the substrate.

Spin-orbit torques in antiperovskite Fe4N pseudo-single-crystal films with negative spin polarization

The spin-orbit torque (SOT) damping-like (field-like) effective fields and efficiencies, HDL(FL) and ξDL(FL), for the MgO substrate/Fe4N (3 nm)/W (5 nm)/cap metallic heterostructure were determined using harmonic Hall and spin-Hall magnetoresistance (SMR) measurements at various temperatures (T). The resistivity of the W layer was measured to be 40 μΩ cm, suggesting a mixed phase of α and β. The sizable anomalous Nernst component was extracted, and a strong T dependence was found. The resultant ξDL(FL) was estimated to be 0.035 (0.015) at T = 300 K, and 0.045 (0.005) at T = 4 K. The longitudinal MR measurements revealed the negative spin polarization of the conduction electrons in the Fe4N layer. However, no sign reversal of the SOT was observed, as in the case where a CoFeB layer with positive spin polarization was employed. The T dependence of ξDL estimated from SMR measurements was in good agreement with that obtained through harmonic Hall measurements, which was indicative of the sizable spin current injection at the Fe4N/W interfaces due to the spin-Hall effect.

Extremely Large Magnetization and Gilbert Damping Modulation in NiFe/GeBi Bilayers

We have fabricated NiFe/GeBi heterostructures and investigated the spin pumping effect. The GeBi semiconductor film had a remarkable impact of the magnetization of the GeBi/NiFe structure, which may have been caused by the strong spin-orbit coupling of the Bi ions that can affect the torque orientation of NiFe. When a nanometer thick Cu film was inserted in the film structure (GeBi/Cu/NiFe), the coercive force of the new film decreased and the saturation magnetization increased because Cu isolated the coupling between the GeBi and NiFe layers. Ferromagnetic resonance (FMR) measurements showed that the GeBi/Cu/NiFe heterostructure had a reduced Gilbert damping and resonance field , when compared with those of the GeBi/NiFe thin film. This work indicated that the GeBi could be used for adjusting both the magnetization and Gilbert damping constant dramatically.

Magneto-thermal transport behavior in freestanding Ni80Fe20/Au bilayer thin films

Spin polarization, when induced in a non-ferromagnetic material, can change the underlying material behavior especially if the spin diffusion length is of the same order as the sample dimension such as thickness. In this study, we experimentally demonstrate thermal hysteretic behavior induced by spin polarization in Ni80Fe20 (10 nm)/Au (100 nm) bilayer freestanding sample. The thermal hysteresis behavior is uncovered using magneto thermal characterization based on self-heating 3ω method. The third harmonic voltage shows diverging behavior and thermal hysteresis during cooling and heating of the sample under an applied magnetic field, which is attributed to the spin accumulation. The spin accumulation and thermal hysteresis in Au occurs due to ferromagnetic proximity polarization from Ni80Fe20 layer. The observed hysteresis behavior is also attributed to freestanding thin film structure and absence of substrate effects leading to longer spin diffusion length. This study demonstrates experimental evidence of ferromagnetic proximity polarization and resulting changes in thermal transport behavior in Au thin films.

A Facile Topochemical Preparation of Ni-Fe LDH Nanosheets Array on Nickel Foam Using In Situ Generated Ni2+ for Electrochemical Oxygen Evolution

Herein, we presented a simple one-step method to prepare Ni-Fe layer double hydroxide nanosheets array (Ni-Fe LDH NSA) integrated electrodes under anaerobic condition at room temperature using untreated nickel foam (NF) as substrate and the NiO thin layer thereon as the Ni2+ source. FeSO4 is utilized as Fe source. The amorphous NiO layer on NF can be dissolved in the weak acidic Fe2+ solution. NH4HCO3 is added to adjust the pH value for controlled hydrolysis of Ni2+ and Fe2+ became brucite to LDH after exposed on the air. Fe-O-Fe and Ni-O-Fe moieties can be lead in during this facile topochemical preparation of Ni-Fe LDH. The structure of electrodes was characterized by SEM, TEM, XPS, XRD, etc. The OER performance of the integrated electrode was tested by a series of electrochemical measurement. The prepared integrated electrode Ni-Fe LDH/NF shows good OER performance with relatively low overpotential (198 mV at 10 mA cm−2), moderate tafel slope (70 mV dec−1) and high electrochemical stability.

Investigation of magnetization dynamic damping in NiFe/Pd bilayer at room temperature

We report the magnetization dynamics behavior of NiFe/Pd bilayer structure by varying the thickness of NiFe layer using broadband ferromagnetic resonance set up. We found linear dependence of the Gilbert damping parameter (α) with the inverse of thickness of FM (NiFe) layer, which indicates possible signature of spin pumping. The calculated value of spin mixing conductance is found to be 1.47×1019m-2. The saturation magnetization of NiFe in NiFe/Pd samples are found to be 1.34±0.03.

Autogenous growth of the hierarchical V-doped NiFe layer double metal hydroxide electrodes for an enhanced overall water splitting.

NiFe layer double metal hydroxide nanosheets (NiFe LDHs) have been extensively investigated as one of the best promising candidates to construct efficient bifunctional catalysts. In this research, element (vanadium) doping into NiFe LDHs grown in nickel foam were synthesized by the one-step method and applied in overall water splitting. The content and structure of the composites were adjusted to regulate the catalyst's electronic structure and reduce the onset potential and achieved unprecedented electrocatalysis for OER and HER. The V-NiFe-LDH/NF showed perfect OER and HER activities with low Tafel slopes of 31.3 and 89.8 mV dec-1, and small overpotentials of 195 and 120 mV at 10 mA cm-2 in 1.0 m KOH solution, respectively. Electrochemical analysis indicated that the efficient catalytic activity of V-NiFe-LDHs/NF mainly benefited from V doping, which optimized the electronic structure and produce defects, thereby resulting in an enhanced conductivity, facile electron transfer, and adequate active sites.

Polyoxometalate intercalated NiFe layered double hydroxides for advanced water oxidation

Exploring high efficient and cost-effective electrocatalysts for oxygen evolution reaction is a determination step towards sustainable green energy applications. Polyoxometalates and layered double hydroxide materials are suggested to be potential catalyst materials; however, those electrocatalytic behaviors are greatly inferior to the state-of-the-art OER electrocatalysts (RuO2 and IrO2). In this work, we employ a self-assembly approach in which polyoxometalate anions are successfully intercalated into NiFe layered double hydroxide. Upon analysis of the composition, the elemental valence state and the infrared spectrum, it confirms that the intercalated polyoxometalate anions in the layers of NiFe layered double hydroxide are in the format of PW12O403−. Even though the partial anions in the as-prepared intercalation NiFe layered double hydroxide are only polyoxometalate anions, its electrochemical performance surpasses the counterpart precursor NiFe layered double hydroxide (NO3−) in many aspects, such as turnover frequencies, overpotentials, kinetics, and stability. The introduction of polyoxometalate anions can optimize the local electronic structure which enhances the charge transport capacity of NiFe layered double hydroxide as well as alter the adsorption/desorption nature of the intermediates during the catalysis process. This work provides a new strategy to boost the OER activity of layered double hydroxide-based electrocatalysts.

Distinct Detection of Thermally Induced Spin Voltage in Pt/WS2/Ni81Fe19 by the Inverse Spin Hall Effect.

Conversion of heat into a spin current by means of the spin Seebeck effect (SSE) is one of the exciting topics in spin caloritronics. By use of this technique, the excess heat may be transformed into a valuable electric voltage by coupling SSE with the inverse spin Hall effect (ISHE). In this study, a thermal gradient and an in-plane magnetic field are used as the driving power to mobilize the spin electrons to produce SSE. A spin voltage is detected by ISHE in the Ni81Fe19 heterostructure by means of a WS2/Pt strip. Using WS2 sheets of different thicknesses, we obtained a large spin Seebeck coefficient of 0.72 μV/K, which is 12 times greater than the conventional spin Seebeck coefficient observed in Pt/Ni81Fe19 bilayer devices. We observe the thickness dependence of tungsten disulfide (WS2) flakes and the polarity reversal of pure SSE signals that are measured without influence from the other thermoelectric effects in our Pt/WS2/Ni81Fe19 device-the most intriguing feature of this study. Without the electric charge conduction, the spins are distributed over a longer distance that is greater than the spin diffusion length of the Ni81Fe19 layer. Such features are strongly desired for designing the efficient spin-caloritronics devices that may be used in the thermoelectric spin generators and the temperature sensors such as thermocouples.

Metal/metal-oxide thin layer heterostructure by laser treatment for memristor application

Metal-oxide memristors are one of the most important sets of memristors for use as the future memory and computing elements. In this context, developing novel methods for producing metal/metal-oxide thin film heterostructures is demanded. Here, we use a 354 nm pulsed laser for treatment of a thin (40 nm) Ni80Fe20 (Permalloy, Py) layer and observe its memristive characteristics. The laser treatment (LT) resulted in oxidation of the surface of the Py layer and therefore forming a uniform Py/Py-oxide heterostructure. The oxygen vacancy formation and rupture for memristivity mechanism is evidenced by I-V measurement of two samples with different oxide thicknesses. The sample with lower thickness of oxidized Py shows lower voltage threshold and higher ON/OFF ratio. Results show that LT method can be used for producing functional thin memristive layers from metallic materials.

The magnetic interfacial properties of an exchange biased nanocrystalline Ni80Fe20/α-Fe2O3 bilayer studied by polarized neutron reflectometry and Monte Carlo simulation

The strength of exchange bias can be influenced by interface roughness and antiferromagnetic morphology. Here, we studied the interface profile of an exchange biased, nanocrystalline Ni80Fe20/α-Fe2O3 bilayer. Magnetometry determined the bilayer’s exchange bias is observed below a blocking temperature of 75 K. Polarized neutron reflectometry measurements revealed the Ni80Fe20 layer was fully saturated to yield a net-moment of 0.95 μB/atom, while the majority of the Fe2O3 layer exhibited zero net-magnetization with the exception of the interfacial region with an uncompensated moment between 0.5 and 1.0 μB/Fe2O3. Monte Carlo simulations of a ferromagnetic/antiferromagnetic bilayer incorporating a granular antiferromagnet indicate that an extrinsic uncompensated moment of ∼1.0 μB/Fe2O3 can arise from grain boundary disorder. The size of the modeled moment is equivalent to the experimental value, and comparable with previous calculations. Furthermore, unlike intrinsic uncompensated spins, it is found that the disorder-induced moment in the granular antiferromagnet is not destroyed by interface roughness.

Effect of Nano Structured NiFe and NiP Thin Layer Coatings on Structural and Mechanical Properties of Mild Steel

The nano crystalline thin coating of NiFe and NiP C has been successfully carried out by using electroplating technique in order to enhance the structural and mechanical properties of mild steel. The NiFe & NiP thin layers were coated on mild steel at constant current density and pH over a deposition period of 30 minutes. All the coated mild steel samples were subjected to various characterization techniques like X-ray Diffraction method (XRD), Vickers hardness, surface roughness and wear test to reveal the effect of NiFe and NiP on mild steel. The mechanical properties such as surface roughness and wear behavior were investigated by using Stylus profilometer and Pin on disc method. The coated mild steel exhibits enhanced mechanical properties than that of uncoated mild steel. The variations in structural and mechanical properties of coated mild steel were also studied.

Soft X-ray magnetic scattering studies of 3D magnetic morphology along buried interfaces in NiFe/CoPd/NiFe nanostructures

With the continuing interest in new magnetic materials for sensor devices and data storage applications, the community needs reliable and sensitive tools for the characterization of such materials. Soft X-rays tuned to elemental absorption edges are a depth and element sensitive probe of magnetic structure at the nanoscale, and scattering measurements have the potential to provide 3D magnetic structural information of the material. In this work we develop a methodology in transmission geometry that allows one to probe the spatial distribution of the magnetization along the different layers of magnetic heterostructures. We study the in-plane/out-of-plane transition of magnetic domains in multilayer thin film systems consisting of two layers of NiFe top and bottom, and a 50 repeat Co/Pd multilayer in the centre. The experimental data are analysed by simulating scattering data starting from micromagnetic simulations, and we find that the out of plane domains of the Co/Pd multilayer intrude into the NiFe layers to a greater extent than would be expected from micromagnetic simulations performed using the standard magnetically isotropic input parameters for the NiFe layers.

Strain relaxation in epitaxial γ′-Fe4N ultrathin films

To investigate substrate-induced strain effects, we grew epitaxial γ’-Fe4N ultrathin films on three different single crystal substrates, MgO, SrTiO3 (STO), and LaSrAlTa oxide. The lattice mismatch was −9.7%, −2.6%, and −1.5% between the Fe4N layer and the MgO, STO, and LSAT substrates, respectively. Therefore, the strain was varied depending on the substrates. Cross-sectional transmission electron microscopy revealed that the lattice strain of Fe4N layer on the STO and LSAT maintained from the interfaces up to ∼2 nm, note here that we achieved to induce strain for the entire Fe4N film thickness. On the other hand, rapid relaxation appeared through many misfit dislocations in the case on MgO. The strain effects in the ultrathin Fe4N films were confirmed as the different behaviors for both ferromagnetic resonance and anisotropic magnetoresistance. These results broaden the amount of modulation in Fe4N based device properties by strain when we reduce the thickness down to several nanometer, which is a dimension encountered in recent spintronic switching devices.

Effect of NiFe layer thickness on properties of NiFe/Cu superlattices electrodeposited on titanium substrate

NiFe/Cu superlattices having different ferromagnetic NiFe layer thicknesses were grown on polycrystalline titanium substrate from a solution containing nickel, iron and copper ions under potentiostatic control. The NiFe layer thickness of the superlattices was changed from 1.5 to 8 nm while the Cu layer thickness was kept constant at 1 nm. The energy dispersive X-ray analysis revealed that, as the NiFe layer thickness increases, the Ni content of the samples increases, the Cu content decreases and Fe content decreases slightly. NiFe/Cu superlattices were polycrystalline face centred cubic (fcc) structure with NiFe and Cu layers adopting the fcc structure due to the low amount of Fe content in the deposits. The crystal orientation of the superlattices was obtained as {111}. The lattice parameters were calculated and slightly decrease from 0.36012 to 0.35382 nm with increase in the NiFe layer thickness. According to the Scanning Electron Microscopy images, when the NiFe layer thickness increases, the cauliflower region becomes less and then the granular-like regions were seen on the surface of the samples. And, the magnetic measurements showed that the saturation magnetization gradually increased from 12.9 to 291.3 emu/cm3 with increasing NiFe layer thickness from 1.5 to 8 nm, confirming the increase of the Ni contents and decrease of the Cu amount in the superlattices. Also, the coercivities ranging from 25.1 to 63.2 Oe are between the soft and hard magnetic properties. The superlattices having NiFe layer thickness less than 5 nm showed giant magnetoresistance (GMR) while the superlattices having greater NiFe layer thicknesses showed aniotropic magnetoresistance. The GMR values of up to 2% were observed for NiFe/Cu superlattices deposited on titanium substrate. It is seen that this material may have the potential applications in sensor and recording media.

Enhancing Electrocatalytic Activity through Liquid-Phase Exfoliation of NiFe Layered Double Hydroxide Intercalated with Metal Phthalocyanines in the Presence of Graphene.

Earth‐abundant transition‐metal‐based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid‐phase exfoliation by taking advantage of their π‐π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material.

Stainless Steel as A Bi-Functional Electrocatalyst-A Top-Down Approach.

For a hydrogen economy to be viable, clean and economical hydrogen production methods are vital. Electrolysis of water is a promising hydrogen production technique with zero emissions, but suffer from relatively high production costs. In order to make electrolysis of water sustainable, abundant, and efficient materials has to replace expensive and scarce noble metals as electrocatalysts in the reaction cells. Herein, we study activated stainless steel as a bi-functional electrocatalyst for the full water splitting reaction by taking advantage of nickel and iron suppressed within the bulk. The final electrocatalyst consists of a stainless steel mesh with a modified surface of layered NiFe nanosheets. By using a top down approach, the nanosheets stay well anchored to the surface and maintain an excellent electrical connection to the bulk structure. At ambient temperature, the activated stainless steel electrodes produce 10 mA/cm2 at a cell voltage of 1.78 V and display an onset for water splitting at 1.68 V in 1M KOH, which is close to benchmarking nanosized catalysts. Furthermore, we use a scalable activation method using no externally added electrocatalyst, which could be a practical and cheap alternative to traditionally catalyst-coated electrodes.

One-Step Synthesis of NiFe Layered Double Hydroxide Nanosheet Array/N-Doped Graphite Foam Electrodes for Oxygen Evolution Reactions.

Developing cost‐effective and highly efficient oxygen evolution reaction (OER) electrocatalysts is vital for the production of clean hydrogen by electrocatalytic water splitting. Here, three dimensional nickel‐iron layered double hydroxide (NiFe LDH) nanosheet arrays are in‐situ fabricated on self‐supporting nitrogen doped graphited foam (NGF) via a one‐step hydrothermal process under an optimized amount of urea. The as prepared NiFe LDH/NGF electrode exhibits a remarkable activity toward OER with a low onset overpotential of 233 mV and a Tafel slope of 59.4 mV dec−1 as well as a long‐term durability. Such good performance is attributed to the synergy among the doping effect, the binder‐free characteristic, and the architecture of the nanosheet array.

Modification of Nife Layered Double Hydroxide and Photocatalytic Activity

Modifying materials by ions with multiple valence states is an effective way for enhancing their properties. NiFe layered double hydroxides (NiFe LDHs) were prepared by using a hydrothermal method. Efficient LDH photocatalyst was synthesized by the modification of NiFe LDHs with Fe(III). Electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area, photoluminescence spectroscopy, and UV-Vis diffuse reflectance spectroscopy were used to investigate the morphology, crystal structure, and optical properties of the NiFe LDHs. The photocatalytic and adsorption performances were examined in the degradation of methyl orange. NiFe LDHs exhibited higher adsorption property but lower photocatalytic activity. After modification with Fe(III), the introducing of Fe ions and recrystallization of LDHs led to the distance decreasing between NiFe LDH sheets and exhibit higher photocatalytic performance.