NiFe Films Research Articles

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.

Influence of electrodeposition parameters on structure and micromechanical properties of thin Ni–Fe films

The correlation between the synthesis modes, chemical composition, crystal structure, surface microstructure, and also the mechanical properties of thin nanostructured Ni – Fe films has been studied. Thin Ni–Fe films on the Si with Au sublayer were obtained using electrolyte deposition with different current modes: direct current and three pulsed modes with pulse duration of 1 s, 10–3 and 10–5 s. It is shown that a decrease in the pulse duration to 10–5 s leads to an increase in the film elastic modulus and the hardness due to the small grain size and a large number of grain boundaries with increased resistance to plastic deformation. The effect of heat treatment at 100, 200, 300, and 400 °C on the surface microstructure and micromechanical properties of the films was investigated. An increase in grain size from 6 to 200 nm was found after heat treatment at 400 °C which, in combination with interfusion processes of the half-layer material, led to a significant decrease in hardness and elastic modulus. Ni–Fe films with improved mechanical properties can be used as coatings for microelectronic body for their electromagnetic protection.

Magnetic phase diagram of CrPS4 and its exchange interaction in contact with NiFe

The magnetic phase diagram of the two-dimensional van der Waals magnet CrPS4 and the exchange bias effect of CrPS4 in contact with NiFe film have been investigated. Based on the magnetic measurements, we figure out the relatively low spin-flop field and spin-flip field for CrPS4, both of the spin transition phenomena are strongly affected by the temperature. The perpendicular exchange bias effect is studied in CrPS4 single-crystal flake covered with 5 nm NiFe. Meanwhile, the variation of the cooling field has a great influence on the exchange bias field and coercivity, which is mainly attributed to the competition between the Zeeman energy and the exchange coupling at the interface as well as the formation of the multi-domain state.

Influence of Multilayer Number to Magneto-Impedance Ratio in Electrodeposited [NiFe/Cu]<sub>N</sub> Multilayer

Magneto-impedance ratio of the multilayer [NiFe/Cu)]N study by the number of multilayer. The both sample films of NiFe and Cu are fabricated by electrodeposition methods on a Cu-patterned substrate. The characteristic of magneto-impedance (MI) is performed at room temperature. Magneto-impedance are modified by varying N times (2, 4, 6 and 8) and the measurements frequency. The result show that the typical symetry of the magneto-impedance curve. Then the magneto-impedance (MI) ratio increases with the increase of frequency and N number layers. The increase of the magnetic permeability should address the increase of the MI ratio. Finally, the highest magneto-impedance ratio of 13.79 is obtained for [NiFe (200)/Cu (25)]8 at frequency 100 kHz.

Microstructure and magnetoimpedance studies of NiFe films electrodeposited on ITO substrate: Experiments and simulations

Structure and magnetoimpedance (MI) properties of Permalloy films electrodeposited on Indium Tin Oxide (ITO) coated on glass substrate have been investigated. Microstructure and magnetic measurements confirm the composition and formation of single phase films with varying thickness. The MI values increased from 2.8% to 50%, while the frequency at which maximum MI is observed shifted to lower frequency when thickness of the NiFe film is increased. Present results show that MI is not only weak but also exhibits a sign change in the lower frequency range. It is shown that the magnetoinductive component is dominant at lower frequencies. Thickness and frequency dependence of MI values are compared with numerically calculated results on the basis of Maxwell’s and Landau- Lifshitz equations. It is found that the thickness and effective conductivity of the film play a significant role in variation of MI values. We have attempted to extract the relative magnetic permeability (μr), the damping factor (α), the angle between the equilibrium state of magnetization and easy axis (θ) and the magnetic anisotropy field (Hk) by fitting the experimental MI data to the standard equations. Experimental results are consistent with the physical parameters obtained from the phenomenological model. The relative permeability values extracted from the MI data corroborate well with magnetic measurements of literature.

Sustained coherent spin wave emission using frequency combs

We demonstrate sustained coherent emission of spin waves in NiFe films using rapid demagnetization from high repetition rate femtosecond laser pulse trains. As the pulse separation is shorter than the magnon decay time, magnons having a frequency equal to a multiple of the 1 GHz repetition-rate are coherently amplified. Using scanning micro-Brillouin Light Scattering (BLS) we observe this coherent amplification as strong peaks spaced 1 GHz apart. The BLS counts vs. laser power exhibit a stronger than parabolic dependence consistent with counts being proportional to the square of the magnetodynamic amplitude, and the demagnetization pulse strength being described by a Bloch law. Spatial spin wave mapping demonstrates how both localized and propagating spin waves can be excited, and how the propagation direction can be directly controlled. Our results demonstrate the versatility of BLS spectroscopy for rapid demagnetization studies and enable a new platform for photo-magnonics where sustained coherent spin waves can be utilized.

The Effect of Heat Treatment on the Microstructure and Mechanical Properties of 2D Nanostructured Au/NiFe System.

Nanostructured NiFe film was obtained on silicon with a thin gold sublayer via pulsed electrodeposition and annealed at a temperature from 100 to 400 °C in order to study the effect of heat treatment on the surface microstructure and mechanical properties. High-resolution atomic force microscopy made it possible to trace stepwise evolving microstructure under the influence of heat treatment. It was found that NiFe film grains undergo coalescence twice—at ~100 and ~300 °C—in the process of a gradual increase in grain size. The mechanical properties of the Au/NiFe nanostructured system have been investigated by nanoindentation at two various indentation depths, 10 and 50 nm. The results showed the opposite effect of heat treatment on the mechanical properties in the near-surface layer and in the material volume. Surface homogenization in combination with oxidation activation leads to abnormal strengthening and hardening-up of the near-surface layer. At the same time, a nonlinear decrease in hardness and Young’s modulus with increasing temperature of heat treatment characterizes the internal volume of nanostructured NiFe. An explanation of this phenomenon was found in the complex effect of changing the ratio of grain volume/grain boundaries and increasing the concentration of thermally activated diffuse gold atoms from the sublayer to the NiFe film.

Bending Strain-Tailored Magnetic and Electronic Transport Properties of Reactively Sputtered γ'-Fe4N/Muscovite Epitaxial Heterostructures toward Flexible Spintronics.

The strain modulation on the magnetic and electronic transport properties of the ferromagnetic films is one of the hot topics due to the practical applications in flexible and wearable spintronic devices. However, the large strain-induced saturation magnetization and resistance change is not easy to achieve because most of the ferromagnetic films deposited on flexible substrates are polycrystalline or amorphous. Here, the flexible epitaxial γ'-Fe4N/mica films are fabricated by facing-target reactive sputtering. At a tensile strain with a radius of curvature (ROC) of 3 mm, the saturation magnetization (Ms) of the γ'-Fe4N/mica film is tailored significantly with a maximal variation of 210%. Meanwhile, the magnetic anisotropy was broadly tunable at different strains, where the out-of-plane Mr/Ms at a tensile strain of ROC = 2 mm is six times larger than that at the unbent state. Besides, the strain-tailored longitudinal resistance Rxx and anomalous Hall resistivity ρxy appear where the drop of Rxx (ρxy) reaches 5% (22%) at a tensile strain of ROC = 3 mm. The shift of the nitrogen position in the γ'-Fe4N unit cell at different bending strains plays a key role in the strain-tailored magnetic and electronic transport properties. The flexible epitaxial γ'-Fe4N films have the potential applications in magneto- and electromechanical wearable spintronic devices.

Observation of Gyromagnetic Spin Wave Resonance in NiFe Films.

This Letter demonstrates spin wave resonance (SWR) owing to the gyromagnetic effect by propagating a Rayleigh-type surface acoustic wave (R-SAW) through ferromagnetic thin films. The SWR amplitude in a NiFe film shows a higher-order frequency variation than in a magnetoelastic Ni film. This frequency dependence is well understood in terms of the presence of a gyromagnetic field attributable to the local lattice rotation in the R-SAW. From the frequency dependence of the SWR amplitude, the gyromagnetic SWR could be separated from another SWR caused by a magnetoelastic effect of the ferromagnet.

Realizing large out-of-plane magnetic anisotropy in L10-FeNi films grown by nitrogen-surfactant epitaxy on Cu(001)

Rare-metal free ferromagnetic material $L{1}_{0}$ FeNi with large uniaxial magnetic anisotropy has attracted much attention for broad use of magnetic materials in various applications. While single-crystal films of $L{1}_{0}$ FeNi can be made by layer-by-layer epitaxial growth, magnitude of the uniaxial anisotropy has been lower than expected because of the imperfection of the crystal atomic structure. Here, a nitrogen (N) -surfactant epitaxial growth below 150 K is employed for overcoming interlayer mixing of the atoms at the interface. Ordered $L{1}_{0}$ FeNi films are successfully prepared on the Cu(001) substrate precovered by a ${\mathrm{Ni}}_{2}\mathrm{N}$ monolayer. The role of the N surfactant and the absence of the intermixing among Fe and Ni during the deposition and annealing processes were investigated by scanning tunneling microscopy and x-ray photoemission spectroscopy. Element-specific magnetic properties were in situ studied by soft-x-ray magnetic circular dichroism (XMCD). The observed Fe hysteresis curve and XMCD of the nitrogen-covered Ni/Fe/Ni trilayer indicate an out-of-plane magnetocrystalline anisotropy large enough for dominating the film shape anisotropy. The N-surfactant epitaxy provides a useful method for fabricating well-ordered magnetic materials without rare metals.

RF magnetron sputtered AlCoCrCu0.5FeNi high entropy alloy (HEA) thin films with tuned microstructure and chemical composition

Abstract High entropy alloy (HEA) thin films are extensively studied recently due to their propensity to display a combination of excellent properties such as high hardness, hydrophobicity, superior oxidation and corrosion resistance. Sputter deposition of thin films comprised of several elements typically requires the use of targets containing multiple elements, making both the stoichiometry and microstructure of the resulting films strongly dependent on the process parameters. In this study, HEA thin films of AlCoCrCu0.5FeNi were deposited at various radio frequency (RF) powers, from 200 to 300 W, to reveal how the power affects composition, microstructure and physical properties. X-ray diffraction (XRD) indicated a mixed phase of FCC and BCC and transmission electron microscopy (TEM) data revealed the presence of amorphous phases between the grain boundaries. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) respectively showed an increase in grain size and surface roughness with increasing RF power. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Al2O3 and Cr2O3 protective oxide layers on the surface of all the HEA films. The highest concentration of Al (19.7%) was detected by energy dispersive spectroscopy (EDS) in the film deposited at the lowest power, which also had the highest nanoindentation hardness of 13 GPa. The hardness dropped to 4.5 GPa as power increased due to a reduction in Al concentration and an increase in average grain size. The film deposited at the highest power showed the highest hydrophobicity with a contact angle of 129°, while the lowest resistivity of 414 μΩ-cm was recorded for the sample deposited with the lowest power. This study shows the influence of deposition power on the microstructure and composition of the HEA thin films, demonstrating that the power can be an effective processing parameter to control various properties of AlCoCrCu0.5FeNi films. An understanding of how key process parameters affect the resulting thin film properties will enable application specific process optimization.

Method of Surface Energy Investigation for Nanostructured Materials: Application to Control NiFe Films Growth Mechanism

Method of Surface Energy Investigation for Nanostructured Materials: Application to Control NiFe Films Growth Mechanism

Spin-pump-induced spin transport in a thermally-evaporated pigment-red film

We report the spin transport properties in a pigment-red (perylene-3,4,9,10-tetracarboxylic dianhydride: PTCDA) film prepared by thermal evaporation. In a palladium (Pd)/PTCDA/Ni80Fe20 tri-layer sample, a pure spin-current is generated in the PTCDA layer by using the spin-pumping driven by the ferromagnetic resonance of the Ni80Fe20 film. The generated spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the spin transport in a PTCDA film, and it is confirmed that a PTCDA film is useful not only as a robust protection layer material but also as a spintronic material.

Terahertz excitation of spin dynamics in ferromagnetic thin films incorporated in metallic spintronic-THz-emitter

An experimental approach to trigger ultrafast spin dynamics at frequencies of the terahertz (THz) regime is explored by directly incorporating ferromagnetic Ni80Fe20 films to a Fe/Au spintronic-THz-emitter. It is found that Ni80Fe20 magnetization is directly coupled to the terahertz magnetic fields, in which the magnetic responses of Ni80Fe20 are phase-locked with terahertz pulses. High efficiency of metallic spintronic-terahertz emitters in driving terahertz-induced magnetization dynamics is observed; the maximum precession amplitude of the out-of-plane component of the Ni80Fe20 magnetization reaches over 10% of its saturation magnetization. Analytical integrations of THz magnetic field pulses reproduce the experimental results, confirming that the underlying mechanism of the observed spin dynamics is the Zeeman coupling between the terahertz magnetic field and magnetization in the Ni80Fe20 film. Our results open up possibilities for the studies of terahertz spin dynamics by integrating highly efficient low-cost metallic spintronic-THz-emitters into magnetic thin film elements.

Tunable high-frequency magnetic properties of NiFe films on triangular wave-like surface of Al2O3 substrate

To tune high-frequency properties, NiFe films are fabricated on triangular wave-like surface of Al2O3 substrate by magnetron sputtering. Faceting, the transformation of a planar surface into two or more surfaces, can be observed on m-plane Al2O3 substrate via annealing process and further format the continuous periodic triangular wave-like structure. The wavelength and oscillation can be adjusted by annealing temperature and time. The magnetic anisotropy field (Hk) of the magnetic film is increased to 320 Oe and the resonance frequency (fr) also has a big improvement to 5.4 GHz. These changes are mainly attributed to the dipolar interaction between surface magnetic charges in the studied system. We prove that high-frequency properties of the soft magnetic film can be controlled by designing a nanoscale periodic triangular wave-like morphology on film surface.

Magnetization of Fe4N thin films: Suppression of interfacial intermixing using buffer layers

We studied the magnetization (Ms) of 60 nm thick polycrystalline Fe4N thin films deposited using reactive dc magnetron sputtering. The optimum substrate temperature (Ts) to grow an stoichiometric Fe4N phase is about 673 K, in agreement with earlier works. However, at this Ts, we found that significant intermixing is taking place at the substrate-film interface, affecting the Ms of Fe4N film, adversely. We performed secondary ion mass spectroscopy (SIMS) measurements to extract the extent of such intermixing. It was found that Si from the SiO2 substrate get interdiffused into Fe4N film forming an undesired interface extending up to almost half of the film. As a result, the average Ms of Fe4N film get reduced by about 25% as compared to its theoretical value. To prohibit such intermixing, we placed thin layers of Ag, Cu, or CrN as a buffer layer between the substrate and Fe4N film. Such buffer layer suppress the extent of interdiffusion remarkably. From SIMS measurements, we found that among all buffer layers, CrN is most suitable as it reduces the extent of intermixing to a minimum level. Magnetization measurements performed using bulk magnetization and polarized neutron reflectivity (PNR) methods also clearly revealed that the Ms was the highest when CrN buffer layer was used. From these results, it becomes apparent that the intermixing taking place at the substrate-film interface plays a vital role in affecting the Ms of Fe4N thin films. To further suppress such intermixing an attempt was also made to bring down the Ts from 673 to 523 K. Obtained results are presented and discussed in this work.

Structure, magnetic and electronic transport properties in antiperovskite cubic γ′-CuFe3N polycrystalline films

The structure, magnetic and electronic transport properties of the facing-target reactively sputtered polycrystalline CuFe3N films have been investigated systematically. The CuFe3N film has a cubic antiperovskite structure. The saturation magnetization satisfied the modified Bloch's spin wave theory. At 300 K, the saturation magnetization of the 80 nm-thick CuFe3N films is 402 emu/cm3, which is smaller than 800 emu/cm3 of the 80 nm-thick polycrystalline Fe4N films. The CuFe3N films are metallic. The anomalous Hall effect in the “dirty region” of σxx < 104 S/cm can be explained by the intrinsic mechanism and the side jump in the proper scaling, which is similar to Fe4N. However, the sign of magnetoresistances in CuFe3N is opposite to that of Fe4N below 20 K because the doped-Cu affects the competition among the Lorentz force, spin-orbit coupling, weak localization and s-d exchange interaction. The small anisotropic magnetoresistance is dominated by the spin-down conduction electron. The transformation from the two-fold to one-fold symmetry in the planar Hall resistivity of the 10-nm-thick-CuFe3N films is related to the competition between the temperature-dependent charge scattering and magnetic-field-dependent spin scattering.

Ultrasound-assisted electrodeposition of Fe-Ni film for OLED mask

Fe-Ni alloy is considered as the most suitable metal for OLED mask making due to its excellent properties. However, electrodeposited Fe-Ni film is often companied with poor surface quality and thermal expansion. To get proper film for masks making, experiments of electroforming Fe–Ni were performed with different ultrasonic powers and current densities. Results show that Fe-Ni film with smooth surface could be electrodeposited at high current density due to the reducing of internal stress of film by ultrasonic power. The iron content, grain size, micro-hardness and Young’s modulus of film all present an upward trend with ultrasonic power increases from 13 W to 93 W, and then a downward trend due to the intensively transient cavitation caused by higher ultrasonic power 120 W. With the ultrasonic power of 93 W and current density of 1 A/dm2, a good surface quality of Fe-Ni films with 60.07 wt.% iron content, microhardness 351 HV, Young's modulus 167.5 GPa and CTE 3.38 × 10−6/℃ can be electrodeposited.

Study of the intensity asymmetry in Brillouin light scattering from magnons in FeNi thin films

The Stokes–anti-Stokes intensity asymmetry, observed by Brillouin light scattering from surface magnetic excitations in thin FeNi films, has been studied by replacing substrates with different dielectric constant as well as varying the applied magnetic field and the laser incident angle. The experimental results show that the Stokes–anti-Stokes intensity ratio depends upon the applied magnetic fields, the wave vectors and also the material of the substrates used to support the FeNi films. Most interesting is that for a fixed magnetic field and a fixed wave vector, the intensity ratio is much more significant for the FeNi film deposited on Nb-doped SrTiO3 substrate than that deposited on surface oxidized Si substrate. The phenomenon of the different asymmetry is depending on the dielectric constant of the substrates. The tendency is in agreement with the theory.

The abnormal damping behavior due to the combination between spin pumping and spin back flow in Ni80Fe20/Rut bilayers

The spin pumping effect of the Ni80Fe20/Rut bilayers was studied by ferromagnetic resonance method. A shutter shift technique was adopted to prepare the wedge-like Ru caplayer on the Ni80Fe20 film with homogeneous thickness and damping constant. Thanks to this special preparation method, the very tiny variation of damping constant due to the spin pumping at the Ni80Fe20/Rut interface was precisely measured and extracted from that of Ni80Fe20 films. Comparing with the conventional monotonically approaching saturation curve of damping constant vs. non-magnetic Ru layer thickness tRu, an additional damping peak was observed. The abnormal damping-tRu curves can be understood as the combined action of spin pumping at Ni80Fe20/Rut interface and spin back flow due to the reflection at Ru surface and Ru/Ni80Fe20 interface.