NiFe Films Research Articles

Особенности перемагничивания двухслойной пленочной структуры ЖИГ/FeNi

In this work, the results of magneto-optical and magnetometric measurements carried out on YIG/FeNi film two-layer structures are presented. YIG films were grown by liquid phase epitaxy, and FeNi films were deposited using magnetron sputtering. It has been established that in the YIG/FeNi system the interlayer coupling is mainly due to the magnetostatic interaction.

The influence of saccharin adsorption on NiFe alloy film growth mechanisms during electrodeposition.

This article deals with the effects of current modes on saccharin adsorption during NiFe electrodeposition, and, as a consequence, its effect on chemical composition, crystal structure, and microstructure of deposited films. For this purpose, we obtained NiFe films using direct, pulse, and pulse-reverse electrodeposition modes. The deposit composition, crystal structure, and surface microstructure are studied. Direct current (DC) and pulse current (PC) films have a smooth surface, while a pulse-reverse current (PRC) film surface is covered by a volumetric cauliflower-like microstructure. The mechanism of the film surface development was considered from the point of view of saccharin adsorption and its action as an inhibitor of vertical grain growth during different current modes. During the DC and PC modes, saccharin is freely adsorbed on the growth centers and restrains their vertical growth. Whereas in the case of the PRC electrodeposition, saccharin adsorbs during cathodic pulses and desorbs during anodic pulses. Therefore, its inhibiting action decreases, vertical grain growth rises, and a rougher surface develops.

Magnetoimpedance in electrodeposited NiFe/Cu composite wires: A study on role of in-situ stress

Microstructure, magnetic and magnetoimpedance properties of Ni80Fe20 (Permalloy) films electrodeposited onto a 100 μm copper wire under varying stress have been investigated. It is found that the magnetoimpedance and field sensitivity values decreased by ∼50% and 70% on application of maximum stress 24.9 MPa. Present analysis shows that the crystallite size increases with stress, which in turn controls permeability and MI. The skin depth also seem to depend on microstructural changes which also affects the MI significantly. Comparison of our experimental data to the results obtained from numerical simulations based on Maxwell's and Landau-Lifshitz equations show good agreement. The magnetic measurements are supported by the relative permeability values extracted from the MI data. Present results suggest that MI parameters, such as field sensitivity, MI% and fmax can also be tuned by applying the stress on the sample during preparation.

Microwave excitations and hysteretic magnetization dynamics of stripe domain films

FeNi films with the stripe domain (SD) pattern are prepared by electrodeposition and sputtering methods. The magnetic domain, static magnetic parameters, and quality factor, as well as dynamic properties of the two films, are respectively performed. The results show the magnetizations of the film were dependent on the direction of SD, and the rotation of the SD is lagging behind the magnetization reversal. The microwave properties of the SD emerge dynamic hysteresis before the saturation magnetic field. These microwave properties are selectively excited with acoustic mode, optical mode, and spin-wave mode. The frequency and intensity of different resonance modes of stripe domain are determined by the local magnetization. The magnetization variations and the rotation of SD of different modes are further illuminated by the micromagnetic simulation. The magnetic anisotropy and the resonance intensity of permeability of different modes were finally described by the modified resonance equations.

Tunable resonance frequency of NiFe thin films by oblique deposition

The soft magnetic metal films own potential applications for high frequency magnetic devices. The operating frequency and reliability of the devices depend on the saturation magnetization and resonance frequency of metal films. Increasing the application frequency of the magnetic thin film is extremely challenging. Herein, we deposited a series of NiFe films using electron beam evaporation with various inclination angles, and investigated the surface morphology and magnetic properties, respectively. This paper presents the relationship between surface morphology and inclination angle.

Acupressure mat-like nanostructure with improved SERS performance

Bimetallic nanostructures have attracted much attention to prepare surface-enhanced Raman spectrometry (SERS) substrate. In this study, the problem that magnetic target material was difficult to glow in magnetron sputtering was overcome and the ferro-nickel (NiFe) alloy was uniformly sputtered onto the cicada wing (CW) to make the substrate magnetic. Then, the mass-produced and dense silver nanoparticles (AgNPs) were deposited on NiFe film to further optimize the SERS substrate by improving the method of oil–water interface self-assembly. It was worth mentioning that with the deposition of AgNPs, the SERS intensity was significantly enhanced, and the substrate remained magnetic property, polarization-independence, excellent sensitivity and reproducibility. We also calculated the Raman spectra of probe molecule bound to Ag10 clusters to theoretically verify the performance changes of the substrate observed from experiment. The fabricated SERS substrate not only showed excellent Raman performance, but also had grand application potential in food safety detection.

Effect of V addition on the body-centered cubic to body-centered tetragonal to face-centered cubic structural transformation of N-containing Fe and FeCo films

In this study, the effect of adding V to N-containing Fe and FeCo on the stability of the body-centered tetragonal (bct) structure was investigated. The crystal structures of FeN, FeVN, FeCoN, and FeCoVN films with a thickness of 20 nm were evaluated, and the body-centered cubic to bct to face-centered cubic structural transformation was observed based on the N content. Results indicate that V addition stabilizes the bct structure and the Co content effectively promotes the formation of the bct structure. The uniaxial magnetic anisotropy of approximately 1.0 MJ/m3 was obtained in the FeCoVN films with the bct structure.

Anomalous Growth of Fe-Ni on Au (111) Chemical Insight from Structural Evidence

The electrodeposition of Fe-Ni alloys usually develops a deposit that is more Fe-rich than the electrolyte. The preferential deposition of the less noble element, often encountered among Fe-group alloys, was introduced by A. Brenner as anomalous codeposition [1]. More recently, it was revealed that the transient growth of Fe-Ni develops a deposit that is even more Fe-rich than the steady-state growth, and leads to a composition gradient along the growth direction [2]. This work is focused on the electrodeposition of Fe-Ni on Au (111) substrate in order to leverage the established knowledge of epitaxial growth of Fe on Au (111) [3]. Transmission electron microscopy was used to investigate the Fe-Ni / Au (111) cross section (Figure 1). The work to be presented will demonstrate how chemical insight about the transient growth can be conjectured based on structural evidence, such as the orientation relationship between the substrate and the electrodeposit. Adding onto the existing theories based on the adsorption of the intermediate electroactive species [4], we attempt to provide insight on the mechanism leading to the composition gradient developed during the transient growth of Fe-Ni on Au (111).[1] A. Brenner, Electrodeposition of Alloys, Academic Press, Cambridge, MA (1963).[2] K. Neuróhr, A. Csik, K. Vad, G. Molnár, I. Bakonyi, L. Péter, Electrochimica Acta 103 (2013) 179-187.[3] Q. Lin, E. Hoglund, G. Zangari, Electrochimica Acta 338 (2020) 135876.[4] I. Tabakovic, J. Gong, S. Riemer, M. Kautzky, J. Electrochem. Soc. 162 (3) (2015) D102-D108. Figure 1. Cross section transmission electron microscopy image of an Fe-Ni thin film electrodeposited on Au (111) substrate. Courtesy: the figure was published in Electrochimica Acta 338 (2020) 135876. Figure 1

Tunable non-Gilbert-type damping in Ni80Fe20 films sputtered on the rippled Al2O3 substrates

The ferromagnetic damping and relaxation mechanisms of Ni80Fe20 (NiFe) films sputtered on rippled Al2O3 substrates were investigated by in-plane angular dependence ferromagnetic resonance (FMR) measurements where these rippled Al2O3 substrates were prepared by thermal annealing. The linewidth of intrinsic contribution due to Gilbert damping mechanism and linewidth of extrinsic contribution related to two-magnon scattering (TMS) and inhomogeneous broadening of films were identified by filtering different magnetic relaxation mechanisms of films. The results show that the magnitude of ferromagnetic damping of films deposited on rippled Al2O3 substrates can be manipulated by modifying the ripple morphology of substrates and it is strongly dependent on the angle between the direction of the ripple and the external field. The non-Gilbert-type damping for these films is an adjustable, anisotropic contribution to the overall relaxation. The two-magnon scattering and inhomogeneous broadening act as non-Gilbert damping mechanism in magnetization relaxation and they dominate the variation of total linewidth. This work revealed the tunable magnetization relaxation in films deposited on rippled Al2O3 substrates with different surface morphology formed by annealing and it would be helpful for utilizing these rippled substrates to design magnetization relaxation characteristics of spintronic and magnonic devices.

Meander Thin-Film Biosensor Fabrication to Investigate the Influence of Structural Parameters on the Magneto-Impedance Effect

Thin-film magneto-impedance (MI) biosensors have attracted significant attention due to their high sensitivity and easy miniaturization. However, further improvement is required to detect weak biomagnetic signals. Here, we report a meander thin-film biosensor preparation to investigate the fabrication parameters influencing the MI effect. Specifically, we hypothesized that an optimal film thickness and sensing area size ratio could be achieved to obtain a maximum MI ratio. A meander multilayer MI biosensor based on a NiFe/Cu/NiFe thin-film was designed and fabricated into 3-, 6-, and 9-turn models with film thicknesses of 3 µm and 6 µm. The 9-turn biosensor resembled the largest sensing area, while the 3- and 6-turn biosensors were designed with identical sensing areas. The results indicated that the NiFe film thickness of 6 µm with a sensing area size of 14.4 mm2 resembling a 9-turn MI biosensor is the optimal ratio yielding the maximum MI ratio of 238%, which is 70% larger than the 3- and 6-turn structures. The 3- and 6-turn MI biosensors exhibited similar characteristics where the MI ratio peaked at a similar value. Our results suggest that the MI ratio can be increased by increasing the sensing area size and film thickness rather than the number of turns. We showed that an optimal film thickness to sensing area size ratio is required to obtain a high MI ratio. Our findings will be useful for designing highly sensitive MI biosensors capable of detecting low biomagnetic signals.

Measuring spin wave resonance in Ni100 x Fe x films: compositional and temperature dependence

We study the composition and temperature dependence of the spin wave resonance in NiFe films, where, x is 40% or below, with a thickness of 100 nm using a temperature variable broadband ferromagnetic resonance (FMR) spectroscopy. From the uniform FMR mode, the saturation magnetization and the Gilbert damping are measured, and using the first perpendicular standing spin wave mode, the exchange stiffness constant is determined. At lower temperatures, we measure an increase of both and A, while α shows a very weak temperature dependence. We find that follows perfectly Bloch’s law, while A is best described by a T 2 law. Additionally, we measure a linear increase in and A with the increase of Fe content in films, while α strongly decreases. The compositional variation of α and A can be ascribed to the increase of in Fe-rich films. Furthermore, we estimate the exchange length () in NiFe films. We find that is temperature independent, however, a strong decrease of is measured in Fe-rich films. This reduction is inversely proportional to .

Host, Suppressor, and Promoter—The Roles of Ni and Fe on Oxygen Evolution Reaction Activity and Stability of NiFe Alloy Thin Films in Alkaline Media

Understanding the oxygen evolution reaction (OER) activity and stability of the NiFe-based materials is important for achieving low-cost and highly efficient electrocatalysts for practical water splitting. Here, we report the roles of Ni and Fe on the OER activity and stability of metallic NiFe and pure Ni thin films in alkaline media. Our results support that Ni(OH)2/NiOOH does not contribute to the OER directly, but it serves as an ideal host for Fe incorporation, which is essential for obtaining high OER activity. Furthermore, the availability of Fe in the electrolyte is found to be important and necessary for both NiFe and pure Ni thin films to maintain an enhanced OER performance, while the presence of Ni is detrimental to the OER kinetics. The impacts of Fe and Ni species present in KOH on the OER activity are consistent with the dissolution/re-deposition mechanism we proposed. Stability studies show that the OER activity will degrade under prolonged continuous operation. Satisfactory stability can, however, be achieved with intermittent OER operation, in which the electrocatalyst is cycled between degraded and recovered states. Accordingly, two important ranges, that is, the recovery range and the degradation range, are proposed. Compared to the intermittent OER operation, prolonged continuous OER operation (i.e., in the degradation range) generates a higher NiOOH content in the electrocatalyst, which is likely related to the OER deactivation. If the electrode works in the recovery range for a certain period, that is, at a sufficiently low reduction potential, where Ni3+ is reduced to Ni2+, the OER activity can be maintained and even improved if Fe is also present in the electrolyte.

Structure, electrical, optical and magnetoelectric properties of magnetron sputtered nanocrystalline NiFe/BaTiO3 thin films

BaTiO3 (BTO) and NiFe films grown on SrTiO3 (STO), Nb:SrTiO3 (NSTO), and ITO-glass substrates were prepared by radio-frequency (RF) and direct-current (DC) magnetron sputtering, respectively. The microstructure, ferroelectricity, leakage current, magnetoelectric (ME) coupling, ultraviolet–visible light spectrum, optical band gap, ellipsometry spectrum and surface morphology of the composite film are characterized by XRD, ferroelectric analyzer, ME coupling test system, U-4100, Horiba Smart SE and AFM. In addition, the stress, strain and piezoelectric voltage of the magnetoelectric composite film under the action of DC and AC magnetic fields are simulated by COMSOL multiphysics software. The experimental results show that the prepared composite film is polycrystalline, the surface roughness of the film is better, and the particles are uniform. The magnetoelectric coupling voltage gradually increases with the increase of the value of the DC magnetic field and the frequency of the AC magnetic field, and it has a larger absorption (about 0.3) at 340 nm. In addition, the simulation results also show the relationship between the coupling voltage VME and the applied magnetic field H.

Second harmonic generation in thin permalloy film

Second harmonic generation versus strength and direction of the applied static magnetic field was measured for a thin permalloy (Ni80Fe20) film in a microstrip line at a driving frequency of 1 GHz and maximum input power of ∼110 mW. The measurements revealed two peaks in the double frequency signal—in the low static field (∼10 Oe) and the high one (∼45 Oe). To explain these findings, a macrospin model of a thin magnetic film with in-plane uniaxial magnetic anisotropy was considered. A perturbation expansion of the Landau–Lifshitz–Gilbert equation provided an explanation of the experimental data. The analysis of the model revealed that the low-field peak was caused by the longitudinal second-order magnetization component and the high-field peak by the transversal one. It was also shown that the uniaxial magnetic anisotropy of the film and the dependence of the magnetic damping parameter on the applied field play an important role in the process of the second harmonic generation. The results obtained give insights into some peculiarities of the nonlinear magnetization dynamics that are important in the development of magnetic film-based devices in the field of microwave signal processing and manipulation.

An energy harvesting technology controlled by ferromagnetic resonance

We have successfully demonstrated electrical charging using the electromotive force (EMF) generated in a ferromagnetic metal (FM) film under ferromagnetic resonance (FMR). In the case of Ni80Fe20 films, electrical charge due to the EMF generated under FMR can be accumulated in a capacitor; however, the amount of charge is saturated well below the charging limit of the capacitor. Meanwhile, in the case of Co50Fe50, electrical charge generated under FMR can be accumulated in a capacitor and the amount of charge increases linearly with the FMR duration time. The difference between the Ni80Fe20 and Co50Fe50 films is due to the respective magnetic field ranges for the FMR excitation. When the FM films were in equivalent thermal states during FMR experiments, Co50Fe50 films could maintain FMR in a detuned condition, while Ni80Fe20 films were outside the FMR excitation range. The EMF generation phenomenon in an FM film under FMR can be used as an energy harvesting technology by appropriately controlling the thermal conditions of the FM film.

Y3Fe5O12 hybrid spin valves with appreciable spin Seebeck effect under perpendicular temperature gradient

Significant thermal voltage signals from spin Seebeck effect and conventional anomalous Nernst and anomalous Righi–Leduc effects have been recognized in the yttrium iron garnet Y3Fe5O12 (YIG)/Cu/NiFe/IrMn hybrid spin valves under a perpendicular temperature gradient. The spin transport characteristic parameters of the soft NiFe film can be quantitatively evaluated, including the spin diffusion length and spin Hall angle. The present results show the significance of the YIG hybrid spin valve structure in exploring various spin dependent phenomena.

Magnetic anisotropic of thermally evaporated FeNi thin film: A soft X‐ray magnetic circular dichroism study

FeNi film was fabricated on Cu/MgO (001) substrates using thermal evaporation technique of a FeNi target to realize the formation of an L10‐FeNi phase. The magnetic anisotropy of FeNi film was systematically investigated by means of X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD) techniques. Our L‐edge XAS and XMCD analysis is performed for 30‐nm FeNi film grown on Cu/MgO (001) substrate. The present experimental results of XAS and XMCD indicate that ~5% Fe atoms are oxidized. Our findings also showed that the orbital magnetic moment of Fe has a significant incident X‐ray angle dependence that exhibits a maximum value at the out‐of‐plane direction corresponding perpendicular to the plane. The origin of anisotropy is successfully explained by element‐specific XMCD technique. The enhancement in magnetic anisotropy energy (MAE) is due to orbital magnetic moments of Fe through spin–orbit interaction. The uniaxial anisotropy energy showed quantitatively good agreement with the volume MAE.

Self-diffusion processes in stoichiometric iron mononitride

In this work, we studied atomic self-diffusion and structural phase transformation in a single phase iron mononitride (FeN) thin film deposited at an optimized substrate temperature (Ts) of 423 K. At this Ts, the FeN film exhibits a tetrahedral coordination between Fe and N atoms (ZnS-type structure with a lattice parameter of 4.28 Å). The structure of the FeN film was studied by combining x-ray diffraction with Fe and N K-edge x-ray absorption spectroscopy and conversion electron Mössbauer spectroscopy measurements. Self-diffusion of Fe and N was measured using secondary ion mass spectroscopy depth profiling in trilayer structures: [FeN(50 nm)/57FeN(2 nm)/FeN(50 nm)] and [FeN(50 nm)/Fe15N(2 nm)/FeN(50 nm)] deposited on an amorphous quartz substrate using reactive magnetron sputtering. It was found that atomic self-diffusion is strongly associated with thermal stability. Before reaching the phase decomposition temperature, the self-diffusion of N was found to be slower than Fe. Upon phase decomposition, both Fe and N diffuse rapidly, and at this stage, the self-diffusion of N takes over Fe. Within the thermally stable state, slower N diffusion indicates that Fe–N bonds are stronger than Fe–Fe bonds in FeN. This behavior was predicted theoretically and has been evidenced in this work.

Magnetic and Microwave Properties of FeNi Thin Films of Different Thicknesses Deposited Onto Cyclo Olefin Copolymer Flexible Substrates

Thin Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">81</sub> films were deposited by magnetron sputtering technique onto cyclo olefin copolymer (COC) flexible polymer substrates. COC/FeNi(15 nm), COC/FeNi(23 nm), COC/FeNi(25 nm), and COC/FeNi(84 nm) composites were obtained and studied using structural, magnetic, and microwave measurements. COC/FeNi(84 nm) composite, which still had certain transparency insured complete protection with respect to the component of microwave signal polarized along the Gunn diode axis (frequency of 10.52 GHz). Even most thin (15 nm) FeNi film was almost as effective as 84 nm film but having much higher transparency acceptable for microfluidic devices. Obtained results indicate that fabricated flexible composites can be used as effective shielding materials in complex multipurpose devices.

Development of Effective Permeability to Complex Permeability and its Application Taking Account of Demagnetization Factor

Effective permeability taking account of demagnetization factor is widely used in the field of the magnetic engineering. A development of this effective permeability to complex permeability in the high frequency domain is studied. In comparison with the solution of LLG equation, it shows that the permeability in the low frequency domain and the resonance frequency calculated by using demagnetization factor are almost corresponding to those calculated by LLG equation. However, the good agreement is not seen in the resonance absorption peak width. Furthermore, the measured complex permeability of a Ni-Fe film is compared with the calculations by using demagnetization factor.