NiFe Layer Research Articles

Strain engineering for controlled growth of thin-film FeNi L10

FeNi thin films in the L10 phase were successfully grown by magnetron sputtering on HF-etched Si substrates on Cu/Cu100−xNix buffers. The strain of the FeNi layer, , was varied in a controlled manner by changing the Ni content of the Cu100−xNix buffer layer from to , which influenced the common in-plane lattice parameter of the CuNi and FeNi layers. The presence of the L10 phase was confirmed by resonant x-ray diffraction measurements at various positions in reciprocal space. The uniaxial magnetocrystalline anisotropy energy is observed to be smaller (around 0.35 MJ m−3) than predicted for a perfect FeNi L10 sample, but it is larger than for previously studied films. No notable variation in with strain state is observed in the range achieved (), which is in agreement with theoretical predictions.

Magnetic-control-electric and reversal behavior of ZnO/NiFe/ZnO multilayer films

The magnetic-control-electric and corresponding dielectric behavior of the ZnO/NiFe/ZnO multilayer films have been demonstrated by applying an ultrathin bimetallic NiFe inserting layer into ZnO films, and fabricated by radio-frequency magnetron sputtering at room temperature without introducing any oxygen gas during deposition process. At first, a high quality crystalline ZnO(002) textured film was deposited and exhibited a dielectric constant value of around 10 confirmed at room temperature with the Agilent 42941B probe and 4294A impedance meters ranged from 40 Hz to 20 MHz. Once ZnO inserted with a 5 nm-thick NiFe inserting layer, the value of dielectric constant was dramatically increased from 10 to 12.5. This phenomenon can be attributed to redistribute the strongly interface charges between ZnO and NiFe layers and accompany with the relaxation of internal stress of ZnO. On the other hand, the external magnetic field induced dielectric variation can also be clearly observed, and the ZnO film with NiFe inserting layer demonstrates a 0.05%-0.10% dielectric tunability. The magnetic-control-electric and corresponding dielectric behavior of ZnO/NiFe/ZnO multilayers with a single inserting NiFe layer compared with that of pure ZnO film also conclude the magnetoelectric effect in present multilayered structures. Moreover, the grain size of the ZnO films was gradually increased from 32.5 nm to 40.5 nm while inserting with an ultrathin NiFe bimetallic layer. This grain structure transition can be attributed to the lattice misfit between ZnO and NiFe. This research work demonstrates that a single NiFe insering layer can effectively control the dielectric and magnetic characters in the ZnO/NiFe/ZnO multilayered structures and provide valuable multifunctional behaviors for potential novel applications design such as ferroic sensor.

Ni Nanoparticles Decorated NiFe Layered Double Hydroxide as Bifunctional Electrochemical Catalyst

Reducing overpotential and increasing current density remain a great challenge for promoting the application of transition metals-based layered double hydroxides (LDHs). Herein, Ni nanoparticles (∼10 nm) decorated NiFe LDH ultrathin (thickness: ∼2 nm) nanosheets (Ni NP/NiFe LDH) were successfully synthesized which exhibited advanced electrocatalytic activity and long-term stability on both oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The onset potentials for OER and UOR are 1.50 V and 1.34 V, respectively, both are lower than NiFe LDH under the same conditions. Moreover, the peak current density of UOR was 300 mA/cm2, which is much larger than reported precious-metal free UOR catalysts. The excellent catalytic performance of Ni NP/NiFe LDH composite for OER and UOR is proposed to result from the abundant exposed active sites, small charge transfer resistance, and the synergistic effects between NiFe LDH and anchored Ni nanoparticles. This work provides inspiring ideas and helpful guidelines in design of low-cost but highly efficient electrochemical catalysts.

Analyzing the magnetic profile in NiFe/NiO bilayers

The magnetic profile of the Si(100)/NiO(35nm)/NiFe(10nm)/Ta(1nm) sample has been obtained by X-ray absorption spectroscopy (XAS) and the X-ray magnetic circular dichroism (XMCD). Two experimental procedures were used. In the procedure 1, the magnetic depth profile has been determines using samples deposited with different NiFe thicknesses, Si(100)/NiO(35nm)/NiFe(t)/Ta(1nm), t=1,3,5,7,10nm. In procedure 2, the sample (NiFe=10nm), was thinned by several in situ sputtering cycles with Ar+ ions, followed by XAS and XMCD analysis. In both procedures, the calculated magnetic moments values tend to decrease close to interface with the NiO antiferromagnetic (AF) layer, however, this decreasement is more evidenced in the sputtered sample. There is no charge transfer between Ni and Fe in the inner part of the NiFe layer, a reduction of the morb/mspineff has been found at the NiFe/NiO interface. Procedure 1 emerged as the most indicated to analyse the interface region.

Influence of static and dynamic dipolar fields in bulk YIG/thin film NiFe systems probed via spin rectification effect

The characteristics of the static and dynamic components of the dipolar fields originating from a bulk polycrystalline yttrium iron garnet (YIG) substrate are probed by depositing a NiFe (Permalloy) layer on it, which acts as a detector. By measuring dc voltages generated via spin rectification effect (SRE) within the NiFe layer under microwave excitation, we characterize the influence of dipolar fields from bulk YIG on the NiFe layer. It is found that the dynamic YIG dipolar fields modify the self-SRE of NiFe, driving its own rectification voltages within the NiFe layer, an effect we term as non-local SRE. This non-local SRE only occurs near the simultaneous resonance of both YIG and NiFe. On the other hand, the static dipolar field from YIG manifests itself as a negative anisotropy in the NiFe layer which shifts the latter’s ferromagnetic resonance frequency.

Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions for optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.

Direct Detection of Pure ac Spin Current by X-Ray Pump-Probe Measurements.

Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni_{81}Fe_{19}) layer in a Py/Cu/Cu_{75}Mn_{25}/Cu/Co multilayer to pump a pure ac spin current into the Cu_{75}Mn_{25} and Co layers, and then directly probe the spin current within the Cu_{75}Mn_{25} layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu_{75}Mn_{25} layer.

Interface adjustment and exchange coupling in the IrMn/NiFe system

The exchange bias effect was investigated, in the 5–300K temperature range, in samples of IrMn [100Å]/NiFe [50Å] (set A) and in samples with inverted layer-stacking sequence (set B), produced at room temperature by DC magnetron sputtering in a static magnetic field of 400Oe. The samples of each set differ for the nominal thickness (tCu) of a Cu spacer, grown at the interface between the antiferromagnetic and ferromagnetic layers, which was varied between 0 and 2Å. It has been found out that the Cu insertion reduces the values of the exchange field and of the coercivity and can also affect their thermal evolution, depending on the stack configuration. Indeed, the latter also determines a peculiar variation of the exchange bias properties with time, shown and discussed with reference to the samples without Cu of the two sets. The results have been explained considering that, in this system, the exchange coupling mechanism is ruled by the glassy magnetic behavior of the IrMn spins located at the interface with the NiFe layer. Varying the stack configuration and tCu results in a modulation of the structural and magnetic features of the interface, which ultimately affects the spins dynamics of the glassy IrMn interfacial component.

Neighboring-Metallic-Layer-Induced Nonreciprocal Wave Propagation in a Thin Metallic Ferromagnetic Film

Nonreciprocal spin wave propagation, induced by placing a neighboring metallic nonmagnetic layer, has been studied in metallic ferromagnetic thin films. The structure consists of a set of coupled microstrip transmission lines acting as antennas placed over a thin Ni80Fe20 layer. Nonreciprocal propagation of magnetostatic surface waves (MSSWs) has been observed. The nonreciprocal effect is evaluated by the amplitude ratio and the phase difference of the MSSWs traveling in opposite directions. By investigating the correlation between the device structure and the nonreciprocal effects, a maximum of −26.0 dB of the amplitude ratio and −180.0° phase difference were obtained. These results can be applied to optimize the nonreciprocal device.

Hybrid Electrocatalysts: Advances in Hybrid Electrocatalysts for Oxygen Evolution Reactions: Rational Integration of NiFe Layered Double Hydroxides and Nanocarbon (Part. Part. Syst. Charact. 8/2016)

On page 473, Q. Zhang and co-workers review advances in hybrid electrocatalysts concerning synthetic strategies, structural characters, and fundamental insights into the structure-performance relationship for the oxygen evolution reaction.

Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between nonmagnetic materials

The Rashba-Edelstein effect stems from the interaction between the electron's spin and its momentum induced by spin-orbit interaction at an interface or a surface. It was shown that the inverse Rashba-Edelstein effect can be used to convert a spin- into a charge current. Here, we demonstrate that a Bi/Ag Rashba interface can even drive an adjacent ferromagnet to resonance. We employ a spin-torque ferromagnetic resonance excitation/detection scheme which was developed originally for a bulk spin-orbital effect, the spin Hall effect. In our experiment, the direct Rashba-Edelstein effect generates an oscillating spin current from an alternating charge current driving the magnetization precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical detection of the magnetization dynamics is achieved by a rectification mechanism of the time dependent multilayer resistance arising from the anisotropic magnetoresistance.

Electric field control of the exchange spring effect in perpendicularly magnetized FePt/NiFe bilayers

The electric field control of the exchange spring (ES) effect in perpendicularly magnetized bilayers is studied using micromagnetic simulation. The ES bilayer with a total thickness of 20 nm is composed of a FePt layer with perpendicular magnetic anisotropy (PMA) and a NiFe layer with in-plane anisotropy. The thickness ratio between the FePt and NiFe layers (TRFN) is varied. Single-crystal lead zinc niobate-lead titanate (PZN-PT) forms the piezoelectric substrate, and electric fields are applied across the thickness of the substrate to induce in-plane stress. The results reveal that application of a negative electric field E reduces the switching field (HS) and squareness ratio (MR/MS) but enhances the nucleation field (HN), while applying a positive E has a negligible effect on these parameters. When the TRFN is 18:2, an electric field of −2 MV/m reduces HS by 5.5% while MR/MS is maintained at 1. This indicates that when the FePt content is sufficiently large, applying a strong negative E can reduce HS without changing MR/MS. Based on the simulation results, we propose a model for electrically assisted magnetic memory.

Ferromagnetic-resonance induced electromotive forces in Ni81Fe19|p-type diamond

Abstract We report on direct-current (DC) electromotive forces (emfs) in a nickel-iron alloy ( Ni 81 Fe 19 ) | p -type diamond under the ferromagnetic resonance of the Ni81Fe19 layer at room temperature. The observed DC emfs take its maximum around the ferromagnetic resonant frequency of the Ni81Fe19, and their signs are reversed by reversing the direction of an externally-applied magnetic field; it shows that the observed DC emfs are spin-related emfs.

Two-magnon scattering by domain wall induced coupling in Co2MnGe/Au/Py layer systems

Sample inhomogeneities such as interface roughness, impurities, or crystal lattice dislocations can be the cause for two-magnon scattering in ferromagnetic thin films. Using an element specific time-resolved technique, we show experimentally that in CoMnGe/Au/NiFe trilayers the uniform magnetization precession in NiFe (Py) layer can be influenced by magnetic stray fields emerging from the domain walls of micrometer size magnetic ripple domains in the CoMnGe layer. We have found that these stray fields cause a phase shift of the transversal dynamic magnetization component of the precessional motion in the Py layer. We attribute the observed phase slip in precession to the two-magnon scattering process.

Effects of Reflow Time on the Interfacial Microstructure and Shear Behavior of the SAC/FeNi-Cu Joint

Effects of reflow time on the interfacial microstructure and shear strength of the SAC/FeNi-Cu connections were investigated. It was found that the amount of Cu6Sn5 within the solder did not have a noticeable increase after a long time period of reflowing, indicating that the electro-deposited FeNi layer blocked the Cu atoms effectively into the solder area during a long period under liquid-conditions. The ball shear test results showed that the SAC/FeNi-Cu joint had a comparable strength to the SAC/Cu joint after reflowing, and the strength drop after reflowing for 210 s was less than that of the SAC/Cu joint.

Exchange bias training relaxation in spin glass/ferromagnet bilayers

A canonical spin glass (SG) FeAu layer is fabricated to couple to a soft ferromagnet (FM) FeNi layer. Below the SG freezing temperature, exchange bias (EB) and training are observed. Training in SG/FM bilayers is insensitive to cooling field and may suppress the EB or change the sign of the EB field from negative to positive at specific temperatures, violating from the simple power-law or the single exponential function derived from the antiferromagnet based systems. In view of the SG nature, we employ a double decay model to distinguish the contributions from the SG bulk and the SG/FM interface to training. Dynamical properties during training under different cooling fields and at different temperatures are discussed, and the nonzero shifting coefficient in the time index as a signature of slowing-down decay for SG based systems is interpreted by means of a modified Monte Carlo Metropolis algorithm.

Homodyne-detected ferromagnetic resonance of in-plane magnetized nanocontacts: Composite spin-wave resonances and their excitation mechanism

This work provides a detailed investigation of the measured in-plane field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an extended Co/Cu/NiFe pseudo spin valve stack using a nanocontact (NC) geometry. The magnetodynamics are generated by a pulse-modulated microwave current and the resulting rectified dc mixing voltage, which appears across the NC at resonance, is detected using a lock-in amplifier. Most notably, we find that the measured spectra of the NiFe layer are composite in nature and highly asymmetric, consistent with the broadband excitation of multiple modes. Additionally, the data must be fit with two Lorentzian functions in order to extract a reasonable value for the Gilbert damping of the NiFe. Aided by micromagnetic simulations, we conclude that (i) for in-plane fields the rf Oersted field in the vicinity of the NC plays the dominant role in generating the observed spectra, (ii) in addition to the FMR mode, exchange dominated spin waves are also generated, and (iii) the NC diameter sets the mean wavevector of the exchange dominated spin wave, in good agreement with the dispersion relation.

Advances in Hybrid Electrocatalysts for Oxygen Evolution Reactions: Rational Integration of NiFe Layered Double Hydroxides and Nanocarbon

The oxygen evolution reaction (OER) has attracted tremendous explorations in both fundamental and application fields recently, due to its core status in next‐generation energy conversion and storage technologies, such as water splitting and metal‐air batteries. Transition metal‐based compounds, especially the NiFe layered double hydroxides (NiFe LDHs) have been well‐established as the most effective and cost‐efficient electrocatalysts to boost the sluggish water oxidation and improve the energy efficiency. Nevertheless, a favorable substrate is highly required to expose the poorly conductive active phases and enhance reactivities of OER. In this review, the recent advances concerning synthetic strategies, hierarchical structures, and OER performances of NiFe LDH/nanocarbon hybrid electrocatalysts are summarized. A brief description of OER catalysis, LDHs, and nanocarbon materials is presented firstly, followed by a thorough overview of various investigations according to their synthetic methods and structural characters. The development of high‐performance OER catalysts is covered by both a short summary and a presentation of future prospects. This review provides stimulatory knowledge and sheds fresh light into the development of advanced functional materials with a wise hybridization of active phases and conductive substrates.

Magnetoimpedance effect of FINEMET ribbons coated with Fe20Ni80 permalloy film

To study the electromagnetic interaction mechanism between different soft magnetic materials, a series of specimen with different thickness Ni80Fe20 film were deposited onto nanocrystalline Fe73.5Cu1Nb3Si13.5B9 ribbons by magnetron sputtering. X-ray diffraction revealed a slightly structural variation of the ribbons as thickness of the Ni80Fe20 film ranging from 0 to 520 nm. The surface roughness of Ni80Fe20 layer was investigated by Atomic Force Microscopy, showing no significant variation with different thickness of Ni80Fe20 layer. The hysteresis loops and the coercivity value indicated the shift of anisotropy direction from parallel to normal to the surface as the Ni80Fe20 thickness increased, thus influencing the magnetic exchange interaction. Compared to the bare Fe73.5Cu1Nb3Si13.5B9 ribbons, coating of Ni80Fe20 films significantly enhanced the giant magnetoimpedance response of the ribbons. The 24% improved GMI ratio was achieved in the ribbon with 260 nm thick Ni80Fe20 film.