NiFe Films Research Articles

Analysis of Magnetization Dynamics in NiFe Thin Films with Growth-Induced Magnetic Anisotropies

We have used angled magnetron sputter deposition with and without sample rotation to control the magnetic anisotropy in 20 nm NiFe films. Ferromagnetic resonance spectroscopy, with data analysis using a Bayesian approach, is used to extract material parameters relating to the magnetic anisotropy. When the sample is rotated during growth, only shape anisotropy is present, but when the sample is held fixed, a strong uniaxial anisotropy emerges with in-plane easy axis along the azimuthal direction of the incident atom flux. When the film is deposited in two steps, with an in-plane rotation of 90 degrees between steps, the two orthogonal induced in-plane easy-axes effectively cancel. The analysis approach enables precise and accurate determination of material parameters from ferromagnetic resonance measurements; this demonstrates the ability to precisely control both the direction and strength of uniaxial magnetic anisotropy, which is important in magnetic thin-film device applications.

The Effect of the Structure of Co–Ni–Fe Films Obtained by Electrochemical Deposition on Their Magnetic Properties

The Effect of the Structure of Co–Ni–Fe Films Obtained by Electrochemical Deposition on Their Magnetic Properties

Dipolar induced nonreciprocal magnon hybridization in FeNi/YIG bilayers

We investigated the magnon hybridization behavior in FeNi films, which were deposited on the yttrium-iron garnet (YIG) films by using Brillouin light scattering. Nonreciprocal magnon hybridizations have been detected not only on the mode densities but also the dispersion relations. The perpendicular standing spin wave mode confined in the thickness direction hybridized with the top surface magnetostatic surface spin wave at smaller wave vectors range while hybridized with the bottom surface mode at larger wave vectors range. The dipolar interaction between the FeNi layer and the YIG layer should be the main reason for the nonreciprocal hybridization of the two modes in the FeNi layer. The nonreciprocal hybridization characteristics of FeNi/YIG double-layer magnetic films enrich the nonreciprocal magnon hybridization system and might have potential application in constructing spin wave-based devices.

Magnetic anisotropy of L1[formula omitted] FeNi (001), (010), and (111) ultrathin films: A first-principles study

In previous experiments, L10 FeNi thin films with different surfaces, including (001), (110), and (111), were produced and studied. Each surface defines a different alignment of the crystallographic tetragonal axis with respect to the film’s plane, resulting in different magnetic anisotropies. In this study, we use density functional theory calculations to examine three series of L10 FeNi films with surfaces (001), (010), and (111), and with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our results show that films (001) have perpendicular magnetic anisotropy, while (010) favor in-plane magnetization, with a clear preference for the tetragonal axis [001]. We proposed calling this type of in-plane anisotropy fixed in-plane. A film with a surface (111) and a thickness of four atomic monolayers has a magnetization easy axis almost perpendicular to the plane of the film. As the thickness of the (111) film increases, the direction of magnetization rotates towards a tetragonal axis [001], positioned at an angle of about 45° to the plane of the film. Furthermore, the most significant changes in spin and orbital magnetic moments occur at a depth of about three near-surface atomic monolayers. Ultrathin L10 FeNi films with varying magnetic anisotropies may find applications in spintronic devices.

Synthesis of Few-Layer Hexagonal Boron Nitride for Magnetic Tunnel Junction Application.

Hexagonal boron nitride (hBN), a wide-gap two-dimensional (2D) insulator, is an ideal tunneling barrier for many applications because of the atomically flat surface, high crystalline quality, and high stability. Few-layer hBN with a thickness of 1-2 nm is an effective barrier for electron tunneling, but the preparation of few-layer hBN relies on mechanical exfoliation from bulk hBN crystals. Here, we report the large-area growth of few-layer hBN by chemical vapor deposition on ferromagnetic Ni-Fe thin films and its application to tunnel barriers of magnetic tunnel junction (MTJ) devices. Few-layer hBN sheets mainly consisting of two to three layers have been successfully synthesized on a Ni-Fe catalyst at a high growth temperature of 1200 °C. The MTJ devices were fabricated on as-grown hBN by using the Ni-Fe film as the bottom ferromagnetic electrode to avoid contamination and surface oxidation. We found that trilayer hBN gives a higher tunneling magnetoresistance (TMR) ratio than bilayer hBN, resulting in a high TMR ratio up to 10% at ∼10 K.

Ferromagnetic resonance measurement with frequency modulation down to 2 K.

Ferromagnetic resonance (FMR) spectroscopy is a powerful technique to study the precessional dynamics of magnetization in thin film heterostructures. It provides valuable information about the mechanisms of exchange bias, spin angular momentum transfer across interfaces, and excitation of magnons. A key desirable feature of FMR spectrometers is the capability to study magnetization dynamics over a wide phase space of temperature (T), frequency (f), and magnetic field (B). The design, fabrication, and testing of such a spectrometer, which uses frequency modulation techniques for improved detection of microwave absorption, reduces heat load in the cryostat and allows simultaneous measurements of inverse spin Hall effect (ISHE) induced dc voltages, is described in this paper. The apparatus is based on a 2-port transmitted microwave signal measurement using a grounded co-planar waveguide. The input radio frequency (RF) signal, frequency modulated at a tunable f-band, excites spin precession in the sample, and the attenuated RF signal is measured phase sensitively. The sample stage, inserted in the bore of a superconducting solenoid, allows magnetic field and temperature variability of 0 to ±5T and 2-310K, respectively. We demonstrate the working of this Cryo-FMR and ISHE spectrometer on thin films of Ni80Fe20 and Fe60Co20B20 over a wide T, B, and f phase space.

Quantifying the orbital-to-spin moment ratio under dynamic excitation

The orbital component of magnetization dynamics, e.g., excited by ferromagnetic resonance (FMR), may generate “orbitronic” effects in nanomagnetic devices. Yet, distinguishing orbital dynamics from spin dynamics remains a challenge. Here, we employ x-ray magnetic circular dichroism (XMCD) to quantify the ratio between the orbital and spin components of FMR-induced dynamics in a Ni80Fe20 film. By applying the XMCD sum rules at the Ni L3,2 edges, we obtain an orbital-to-spin ratio of 0.108 ± 0.005 for the dynamic magnetization. This value is consistent with 0.102 ± 0.008 for the static magnetization, probed with the same x-ray beam configuration as the dynamic XMCD experiment. The demonstrated method presents a possible path to disentangle orbitronic effects from their spintronic counterparts in magnetic media.

Photovoltaic effect on silicon–alumina–ferromagnet tunnel junction providing insights about spin-dependent molecular spintronics solar cells

The study focuses on the observation of the photovoltaic (PV) effect on Si/AlOx/FM semiconductor–insulator–ferromagnetic metal (SIFM) structure. Utilization of ∼10 nm NiFe film as the top ferromagnet (FM) layer was permeable for sufficient light radiation necessary for reaching the silicon substrate for the generation of electron–hole pairs upon photoexcitation. The effect of light intensity and magnetic field was studied on the SIFM’s PV response. We also investigated the role of silicon doping and the AlOx tunnel barrier between Si and FM in exploring suitable band bending necessary for separating the electron–hole pairs. Increasing the dopant density in Si and a damaged AlOx tunnel barrier quenched the PV effect. Ferromagnet/Insulator/Ferromagnet (FMIFM) was also studied to gain deeper mechanistic insights into the spin-dependent photovoltaic effect observed on FM/AlOx/FM tunnel junction-based molecular spintronics devices. Bridging of magnetic molecules between the Si and FM electrodes of SIFM increased the overall device current by establishing additional parallel conduction channels along with the AlOx tunnel barrier. However, SIFM with molecular conduction channels did not produce a PV effect. This study reported the PV effect on well-designed SIFM and opened possibilities for exploring new systems. More importantly, this paper provided insights into the role of molecule-induced exchange coupling in transforming an ordinary, cheap, and widely available ferromagnet into a semiconductor-like material capable of showing PV.

Combining annealing temperature and interface engineering for improving anisotropic magnetoresistance in Ta/NiFe/Ta films

Anisotropic magnetoresistance (AMR) sensors are pivotal in various applications due to their low power consumption, scalability, and cost-effectiveness due to the simple sensor structure, comprising one NiFe film, usually encased in a buffer and cap layer. In this work, we explore the effects of inserting MgO and Pt dusting layers between the NiFe sensing layer and adjacent capping and buffer layers, on the electric, magnetic and structural properties of AMR sensors. We describe results on sensors based on Ta/NiFe/Ta, with an as-processed AMR value of 2.0 %. The insertion of Pt thin films had a positive impact, with AMR values increasing to 2.2 %, contrary to the observed with MgO dusting films. Magnetic annealing up to 370 °C caused an increase of the resistivity and reduction in AMR (with Pt dusting layers), on the contrary, MgO dusting layers improved the sensor performance upon annealing, with AMR increasing to 2.5 % (5 h at 370 °C). In light of the findings, the incorporation of Pt and MgO dusting layers enables tailoring the grain size and resistance of Ta/NiFe/Ta films, while combined with proper annealing, which is relevant for applications where Ta and NiFe are available for AMR sensor fabrication.

Temperature-dependence of magnetron sputtered NiFe films: Structure, morphology, optical, electrical and OER catalytic properties

The NiFe films were fabricated on p-type Si, SiO2, SrTiO3 (STO) and Ni foam (NF) substrates to evaluate the structure, morphology, optical, electrical, and catalytic properties of the films fabricated by the direct current (DC) magnetron sputtering (MS) method at different temperatures. The microstructure, morphology, composition, optical, electrical and oxygen evolution reaction (OER) catalytic properties show a strong temperature dependence. The film has a larger absorption 0.575, higher band gap 2.15 eV at larger temperature, better conductivity with the sheet resistance 2.15 Ω/sq at higher temperature, and reaching lower overpotential 290 mV at the current density of 10 mA/cm2, which indicate that the prepared NiFe films are expected to be a candidate for optical, electrical devices and catalysts.

Achieving in-plane biaxial magnetic anisotropy of permalloy films by localized magnetoelastic coupling

Magnetic films with in-plane magnetic anisotropy have been extensively applied in the field of magnetoelectronic devices. Here, we report a control method for the in-plane magnetic anisotropy of Ni80Fe20 films by localized magnetoelastic coupling. Nanotrenches are patterned on Ni80Fe20/polymethyl methacrylate bilayers, and the Young’s modulus mismatch between micro-patterned magnetic/polymer layers directionally releases the local stress. Due to magnetoelastic coupling, the directed tension distribution can rearrange the stripe domain along the patterned nanotrenches and induce the in-plane uniaxial magnetic anisotropy of the Ni80Fe20 films. Using hierarchically patterned tension distributions with 2D nanotrench arrays, in-plane biaxial magnetic anisotropy can be arbitrarily designable in Ni80Fe20 films.

Magnetic Anisotropy of FeNi Multilayer Films with Different Orientations of the Magnetic Anisotropy Axes in Adjacent Layers

FeNi films were prepared using the DC magnetron sputtering technique with an oblique deposition arrangement. Multilayers with different orientations of the magnetic anisotropy axes were obtained thanks to a rotary sample holder inside the vacuum chamber. Magnetic properties were studied using magneto–optical Kerr microscopy and a vibrating sample magnetometer. Single-layered FeNi films having thicknesses as high as 10 nm and 40 nm show in-plane uniaxial easy magnetization axes produced by the oblique incidence of incoming components of the beams. Magnetic anisotropy field for four-layered samples with orthogonal uniaxial magnetic anisotropy axes in the adjacent layers and the thickness of individual layers of 10 nm and 40 nm turned out to be less than in single-layered films. The magnetic properties peculiarities of the eight-layered sample FeNi (10 nm) × 8 obtained by rotation of the sample holder by 45° before deposition of each subsequent layer suggest the formation of a helix-like magnetic structure through the thickness of the multilayered sample similar to the magnetization arrangement in the Bloch-type magnetic domain wall.

Substrates with Different Magnetic Properties Versus Iron-Nickel Film Electrodeposition

Abstract The hereby work presents the iron-nickel alloys electroplated on the different metallic substrates (aluminium, silver, brass) using galvanostatic deposition, with and without presence of the external magnetic field (EMF). The films were obtained in the same electrochemical bath composition - mixture of iron and nickel sulphates (without presence of additives) in the molar ratio of 2 : 1 (Ni : Fe), the electric current density (50.0 mA/cm2), and the time (3600 s). The mutual alignment of the electric (E) and magnetic field (B) was changeable - parallel and perpendicular. The source of EMF was a set of two permanent magnets (magnetic field strength ranged from 80 mT to 400 mT). It was analysed the surface microstructure, composition, morphology, thickness and the mechanical properties (roughness, work of adhesion). The surface morphology and the thickness of films were observed by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). The elemental composition of all FeNi films was measured using Wavelength Dispersive X-Ray Fluorescence (WDXRF). The crystalographic analysis of the deposits was carried out by X-Ray Diffraction. Depending on the used substrate, modified external magnetic field orientation influenced the tribological and physio-chemical properties of the deposited layers. The diamagnetic substrates and EMF application reduced the FeNi thickness and the average crystallites size, in contrast to the paramagnetic substrate. Parallel EMF increased the value of the tribological parameters for CuZn and Ag but decreased for Al. The content of FeNi structure was rising in the case of diamagnetic substrate and the dependence was opposite on the paramagnetic substrate.

Splitting phenomenon of ferromagnetic resonance spectra in NiFe films deposited on periodically rippled sapphire substrates

The splitting phenomenon of ferromagnetic resonance (FMR) spectra of Ni80Fe20 (NiFe) films deposited on periodically rippled sapphire substrates is studied experimentally with the help of micromagnetic simulation. The analyses show that the splitting of FMR spectra is related to the periodic ripple topography of films. When the applied magnetic field is perpendicular to the ripple direction, the effective field of periodically rippled films becomes inhomogeneous. The splitting of FMR spectra originates from localized FMR peaks corresponding to different regions with different effective field intensities in the rippled structure. Furthermore, the relative intensity and position between the split mode and the main FMR mode can be changed by designing ripple topography. This work would help understand the splitting phenomenon of FMR spectra for magnetic thin films deposited on the periodically rippled sapphire substrates.

Flexible, Bending Stable, and Biocompatible Silk Fibroin/NiFe Films for Bio‐Integrated Microwave Applications

AbstractIntegration of magnetic materials into bio‐integrated flexible electronics will bring multi‐functionality, such as magnetoception and wireless communication. In practical application, the performance of magnetic materials and devices should remain stable during cyclic bending–unbending and they can be degradable within a designated lifetime. However, direct integration of magnetic materials with flexible and biocompatible materials and maintaining mechanically stable microwave performance have not been achieved yet. Here, ultrathin (5–50 nm) permalloy (NiFe) films deposited on biocompatible silk fibroin (SF) films are shown to be bending stable, and dissolvable. The ferromagnetic properties of NiFe films deposited on SF, Kapton, and silicon are studied and compared by ferromagnetic resonance. Benefiting from the low surface roughness of fibroin, which is only ≈0.8 nm, SF/NiFe films exhibit comparable ferromagnetic properties to Si/NiFe, better than that of Kapton/NiFe films. Moreover, the ferromagnetic resonance field of SF/NiFe films remains highly stable during cyclic bending that is exposed to both compressive and tensile strain/stress, and its temperature stability is very close to that of Si/NiFe. Finally, the whole SF/NiFe films are demonstrated to be dissolvable and biocompatible. Therefore, SF/NiFe films can be a useful and stable platform for flexible and biocompatible microwave applications.

Cooperative Fe-Sites in Nickel and Cobalt Oxyhydroxides

With incorporated iron, nickel and cobalt oxyhydroxides display the highest known oxygen evolution activities of any catalyst in alkaline media. To leverage this high activity in low temperature electrolysis systems, a comprehensive understanding of where Fe-based active sites form, their local chemical structure, and how this structure evolves under electrochemical conditioning is critical. Here we show that incorporation of Fe into NiOxHy and CoOxHy films during constant potential chronoamperometry yields NiFeOxHy and CoFeOxHy catalysts with extremely high TOFs of up to ~40 s-1 and 0.7 s-1, respectively, at 350 mV overpotential. Further, we discover that the TOF of these materials is linearly related to the amount of Fe incorporated with this method. We propose a mechanism involving cooperative catalysis involving multiple Fe sites to explain this linear dependence. Density functional theory calculations are used to show this cooperativity may arise from increased ability to delocalize oxidative charge in active sites comprised of neighboring FeOxHy monomers. We then show that cycling these films lowers the per-Fe TOF substantially, to a level similar to that of co-deposited NiFe and CoFe films. This loss of activity during cycling and similarity to co-deposited films in which Fe occupies intraplanar lattice sites is consistent with migration of high activity Fe clusters initially adsorbed at surface edges and defects during chronoamperometry to less active sites within the oxyhydroxide lattice via cycling-driven dynamic substrate behavior. Further evidence for this Fe relocation into bulk lattice sites is provided using the redox features of adsorbed Ni2+ and Co2+ as probes for monitoring the extent to which ions are incorporated into the bulk of NiOxHy and CoOxHy.

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films.

The injection of pure spin current into the non-magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (~20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni80Fe20) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin-mixing conductance of ~1.02 1018 m-2, a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy-pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films

AbstractThe injection of pure spin current into the non‐magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (≈20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni80Fe20) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin‐mixing conductance of ≈1.02×1018 m−2, a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy‐pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.

Large magnetostriction in γʹ-Fe4N single-crystal thin film

An Fe4N(110) single-crystal film of 50 nm thickness with γʹ phase is prepared through hetero-epitaxial growth on an MgO(110) single-crystal substrate at 400 °C by reactive sputtering. The out-of-plane and in-plane lattice constants agree with those of bulk within small differences less than 0.2% and the orientation dispersions are about 1.2°. The degree of N site ordering in Fe4N structure is estimated to be 0.995. The arithmetical mean surface roughness is as small as 0.3 nm. These data show that a high-quality Fe4N single-crystal film is successfully formed. The Fe4N film shows in-plane magnetic anisotropy with the easy magnetization direction parallel to [001] and with the hard direction parallel to [1_11], which is reflecting the positive magnetocrystalline anisotropy, K1. A large negative λ100 value of –40 × 10–6 and a fairly-large positive λ111 value of +150 × 10–6 are observed. The present study has shown that γʹ-Fe4N compound is one of the strong candidates for rare-metal-free magnetostrictive materials.

Features of pulse-reverse modes for Ni–Fe nanogranular films electrodeposition: Correlation of structural parameters and MI effect

Through pulse-reverse electrodeposition with various reverse durations, the Ni–Fe films were synthesized. The film's structure was different. With an increase in the reverse duration, the average grain size and porosity increased to a certain point. As the reversal duration is increased, the porosity and average grain size decrease. Magnetic anisotropy was revealed through an analysis of magnetic characteristics. In particular, when the magnetic field was perpendicular to the samples, the remnant magnetization increased from 0.3 to 2.3 emu/g. The remnant magnetization varied from 77 to 91 emu/g with a parallel orientation. Research on the magnetoimpedance has revealed that at a frequency of 100 kHz, the magnetoimpedance coefficient is at a minimum due to resonance effects in both directions of the magnetic field. The magnetostatic model can be used to explain the mechanism of change in the magnetoimpedance in the low-frequency range. The magnetoimpedance occurs in the medium frequency range (from 10 kHz to 1 MHz) due to changes in the magnetic permeability caused by the impact of a magnetic field and an increase in current frequency, which modify the depth of the skin layer.With an increase in current frequency passing through the sample, the current density on the near-surface layer becomes non-uniform. This non-uniformity is significantly influenced by microstructure parameters such as porosity, average grain size, and the degree of texturization, all of which contribute to the conductor's impedance. It opens new direction for smart sensors development.