NiFe Thin Films Research Articles

Role of growth parameters on structural and magnetic properties of Fe4N thin films grown by reactive magnetron sputtering

We studied the effect of growth parameters on the phase formation of Fe4N in a reactive sputtering process. The Fe4N phase formation was found to be extremely sensitive to N2 gas flow and sputter rate but not so much on the substrate temperature. But post-deposition annealing (PDA) time was found to be a critical parameter to get single phase Fe4N. As PDA time increases, the anti-bonding states characteristic of Fe4N start to diminish due to N out-diffusion. Signatures of such N diffusion process can also be seen from the Fe and N depth profiles. We found that the residual resistivity ratio was maximum for the optimized Fe4N films. Magnetization measurements were performed using bulk magnetization as well as polarized neutron reflectivity. We found that the magnetic moment of optimized Fe4N film was about 2.3 μB/atom at 15 K. Magnetic anisotropy measurements carried out using magneto optical-Kerr effect exhibit a rotatable anisotropy.

Structural and magnetic properties of FeN thin films grown on TiN

We studied the growth of iron mononitride (FeN) thin film on a titanium mononitride (TiN) underlayer. FeN samples with a zinc blende (ZB)-type structure were deposited using reactive magnetron sputtering with and without the TiN underlayer on an amorphous quartz substrate. Combining x-ray diffraction, conversion electron Mössbauer spectroscopy, nuclear forward scattering and N K-edge x-ray absorption near edge spectroscopy measurements, we probed the long range and the local structure in our samples. FeN films are known to exhibit structural and magnetic imperfections. With the TiN underlayer such imperfections get reduced to a large extent. By studying films of different thicknesses, the origin of imperfections present in FeN films has turned out to be correlated with the film growth process. Obtained results are presented and discussed in this work.

Investigation of FeN and TiN thin films properties for possible application in electronic devices

In the present work, thin films of FeN (Iron Nitride) and TiN (Titanium Nitride) were deposited in samples of laminated glass by cathodic cage deposition technique using stainless steel and titanium cages, respectively. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Wettability and Electrical Conductivity techniques were used to characterize the samples. To obtain the electrical conductivity values, the electrical resistivity (also known as specific electrical resistance) was calculated. In this way, the lower the resistivity, the easier is the passage of an electric charge through the material. To this purpose, it was used the four-point probes method. FeN film presented hydrophobic surface, and TiN film hydrophilic surface. Both films were promising in electrical conductivity analysis. The results show promise applications in the electronic devices.

Heavy‐Metal‐Free, Low‐Damping, and Non‐Interface Perpendicular Fe16N2 Thin Film and Magnetoresistance Device

Realization of sub‐10 nm spin‐based logic and memory devices relies on the development of magnetic materials with perpendicular magnetic anisotropy that can provide low switching current and large thermal stability simultaneously. In this work, the authors report on one promising candidate, Fe16N2, a heavy‐metal‐free, non‐interface perpendicular magnetic material and demonstrate a perpendicularly magnetized current‐perpendicular‐to‐plane (CPP) giant magnetoresistance (GMR) device based on Fe16N2. The crystalline‐based perpendicular anisotropy of Fe16N2 in the CPP GMR device is measured to be about 1.9 × 106 J m−3 (1.9 × 107 erg cm−3), which is sufficient to maintain the thermal stability of sub‐10 nm devices. A first principle calculation is performed to support this large magnitude of the perpendicular anisotropy. Moreover, the Gilbert damping constant of the Fe16N2 thin film (α ≈0.01) measured by ferromagnetic resonance (FMR) is lower than for most existing materials with crystalline perpendicular magnetic anisotropy. The non‐interface perpendicular anisotropy and low damping properties of Fe16N2 may offer a pathway for future spintronics logic and memory devices.

High saturation magnetization and low magnetic anisotropy Fe-CN martensite thin film

Fe16N2 thin films possess high saturation magnetization (Ms) and high magnetic crystalline anisotropy (Ku) simultaneously. For application in magnetic recording and electrical machine, soft magnetic materials with high Ms and low Ku are desirable. In this report, carbon was doped into FeN thin films. Fe-CN martensite thin films, also named “Minnealloy,” were fabricated by a facing target sputtering system. The Fe-CN martensite phase was detected by X-ray diffraction (XRD). Vibrating sample magnetometry (VSM) measurements confirmed the high Ms property even though ordered Fe-CN was not formed. An X-ray photoelectron spectroscopy study was carried out to reveal the carbon and nitrogen electronic environment. The Ku value was obtained from the M-H loop and the law to approach saturation with reasonable consistency around 1–2 × 106 erg/cc, which is about five to ten times smaller than that of the ordered Fe16N2 thin film (1–2 × 107 erg/cc). The combination of high Ms and low saturation fields makes the Fe-CN martensite thin film a potential candidate for the magnetic write head and other applications.

Simple planar Hall effect based sensors for low-magnetic field detection

Magnetic field sensors based on the planar Hall effect using single layer Ni80Fe20 thin films have been designed, fabricated and characterized. By optimizing the sensor’s dimension, such as the thickness and the length to width ratio, experimental results have shown that the sensor’s sensitivity could be increased up to three times thanks to the enhancement of the shape magnetic anisotropy. The highest sensitivity of 100 μV Oe−1 corresponding to the relative resistance change up to 20 mΩ/Oe was achieved at a supplied DC current of 5 mA for the cross-shaped geometry of the sensor with 5 nm in the thickness and a length/width ratio of 10. Simple structure, low fabrication cost, and low power consumption make this sensor very promising for low field magnetic field sensing such as geomagnetic field detections.

High electrochemical performance of γ″-FeN thin film electrode for lithium ion batteries

Transition metal nitrides are promising alternative anode materials for the next-generation high-energy and high-power lithium ion batteries because of their large specific capacity and superior electronic and ionic conductivity. In this work, nanocrystalline γ″-FeN thin films are prepared by reactive magnetron sputtering and their lithium-storage performance is investigated. The γ″-FeN electrode retains high specific capacities of 1020.4 mAh/g after 100 discharge/charge cycles at the current density of 0.2 A/g and 667.1 mAh/g after 500 cycles at 2 A/g. Even at 10 A/g, a remarkable specific capacity of 469.0 mAh/g is achieved. Scanning and transmission electron microscopic analyses both prove that the microstructure of γ″-FeN thin film is durable against repeated lithiation and delithiation reactions.

Electromagnetic interference shielding effectiveness of sputtered NiFe/Cu multi-layer thin film at high frequencies

We focused on the electromagnetic interference shielding effectiveness of multi-layer thin films, which were composed of Cu and NiFe, fabricated by direct current magnetron sputtering. Crystal structures and microstructures of the multi-layer thin films were confirmed through X-ray diffraction and field emission transmittance electron microscopy. In addition, the magnetic properties of the multi-layer thin films and pure NiFe thin films were measured by using a vibration sample magnetometer and vector network analyzer. To improve the electromagnetic interference shielding effectiveness at high frequencies, we selected Cu and NiFe because of their excellent conductive properties and high permeability. The shielding effectiveness of different types of thin films (Cu, NiFe, NiFe/Cu) with 4 μm thickness was measured from 0.7 GHz to 10 GHz, and the shielding effectiveness of the multi-layer thin films was found to be more efficient than that of Cu and NiFe thin films over the entire high frequency range. In the case of the 4 μm NiFe/Cu multi-layer thin films, an improvement in the shielding effectiveness is attributed to multiple reflections at the NiFe/Cu interfaces of the multi-layer thin films.

Resonant Change in Element Contents and Crystal Structure Change in Co–Ni–Fe Thin Films Electrodeposited Using Rectangular Pulse Current over Megahertz Frequency Range

Resonant Change in Element Contents and Crystal Structure Change in Co–Ni–Fe Thin Films Electrodeposited Using Rectangular Pulse Current over Megahertz Frequency Range

Nanoscale measurement of giant saturation magnetization in α″-Fe16N2 by electron energy-loss magnetic chiral dichroism

Metastable α″-Fe16N2 thin films were reported to have a giant saturation magnetization of above 2200 emu/cm3 in 1972 and have been considered as candidates for next-generation rare-earth-free permanent magnetic materials. However, their magnetic properties have not been confirmed unequivocally. As a result of the limited spatial resolution of most magnetic characterization techniques, it is challenging to measure the saturation magnetization of the α″-Fe16N2 phase, as it is often mixed with the parent α′-Fe8N phase in thin films. Here, we use electron energy-loss magnetic chiral dichroism (EMCD), aberration-corrected transmission electron microscopy, X-ray diffraction and macroscopic magnetic measurements to study α″-Fe16N2 (containing ordered N atoms) and α′-Fe8N (containing disordered N atoms). The ratio of saturation magnetization in α″-Fe16N2 to that in α′-Fe8N is determined to be 1.31 ± 0.10 from quantitative EMCD measurements and dynamical diffraction calculations, confirming the giant saturation magnetization of α″-Fe16N2. Crystallographic information is also obtained about the two phases, which are mixed on the nanoscale.

Grain growth and solid-state dewetting of Bi-Crystal Ni-Fe thin films on sapphire

We studied the solid-state dewetting behavior of thin Ni80Fe20 films deposited on basal plane oriented sapphire substrate and annealed in the range of temperatures of 1023–1323 K. All studied films exhibited strong <111> texture and maze bicrystal microstructure, with only two grains misoriented by 60° around the common <111> axis present in the film. The morphology of partially dewetted films changed from the one typical for polycrystalline thin films to the one typical for single crystalline heteroepitaxial films with increasing temperatures and annealing times. This change of dewetting behavior was associated with the fast grain growth in the films. The films of pure Ni of identical thickness, annealed under identical conditions exhibited significantly slower grain growth and lower thermal stability. Both the high-resolution X-ray diffraction and the cross-sectional high-resolution transmission electron microscopy observations revealed the phase separation of the Ni80Fe20 films into two parallel layers of the face-centered cubic (adjacent to the substrate) and hexagonal close-packed (on the top of the film) phases of similar compositions. Our density functional theory (DFT) calculations indicated that this phase separation is driven by the decrease of the film surface and interface energy, leading to the thermodynamically equilibrium thickness of the metastable hexagonal close-packed phase. This phase exhibits higher surface anisotropy than its stable face-centered cubic counterpart and is instrumental in accelerating the grain growth in the film via suppression of grain boundary grooving.

Influence of Surface Energy on Ni-Fe Thin Films Formation Process

The Ni-Fe thin films were produced via electrodeposition in four different modes - direct current, and three types of pulse-modes with different pulse duration onto Au sublayer. The correlation between technological parameters of the electrodeposition and microstructure was demonstrated. Analysis of microstructure evolution revealed an un-expected changing of the film growth mechanism from “island” to “layer-by-layer” with the decreasing of the grain size less than 10 nm. Explanation was found in binding energies competition, that has been defined using the unique AFM method, based on recording the angle of the cantilever twist, when scanning in contact with the surface.

Evidence of substrate roughness surface induced magnetic anisotropy in Ni80Fe20 flexible thin films

Experimental and computational evidence of a surface roughness induced magnetic anisotropy in NiFe thin films coated onto substrates of various surface roughnesses is reported. Magnetic coercive fields of 15 nm NiFe thin films coated on substrates with approximately 7 nm average roughness were remarkably 233% larger than identical thin films coated onto smooth substrates with < 1 nm average roughness. The NiFe films coated onto rough substrates developed hard and easy axes, normally non-existent in NiFe Permalloy. A linear correlation of the incline angles of the hard axis hysteresis loops to the average roughness values of the individual substrates was observed, with 99% correlation level. Using a modified micromagnetics theory that incorporates the effects of surface roughness, it is shown the observed magnetic anisotropy arises due to the spatial anisotropy of the surface roughness, resulting in an effective in-plane uniaxial magnetic anisotropy with energy density up to 15 kJ/m3.

Thermal analysis on crystal phase synthesis of iron nitride film and its magnetic properties

The phase transition law of Fe-N system is very important for efficiently synthesizing single-phase &lt;i&gt;γ&lt;/i&gt;'-Fe&lt;sub&gt;4&lt;/sub&gt;N thin films. The &lt;i&gt;γ&lt;/i&gt;"-FeN thin films are deposited on silicon wafers via DC reactive magnetron sputtering; some of them are stripped from the silicon wafers and measured by using the synchronous thermal analysis (TG-DSC) for studying the phase transition law of Fe-N system. The results of TG-DSC show that at a heating rate of 10 ℃/min, the Fe-N system has five phase transitions in a temperature range between room temperature (RT) and 800 ℃, i.e. I (330−415 ℃): &lt;i&gt;γ&lt;/i&gt;''-FeN→ξ-Fe&lt;sub&gt;2&lt;/sub&gt;N with an endothermic value of 133.8 J/g; II (415−490 ℃): ξ-Fe&lt;sub&gt;2&lt;/sub&gt;N→ε-Fe&lt;sub&gt;3&lt;/sub&gt;N with no obvious latent heat of phase change; III (510−562 ℃): ε-Fe&lt;sub&gt;3&lt;/sub&gt;N→&lt;i&gt;γ&lt;/i&gt;'-Fe&lt;sub&gt;4&lt;/sub&gt;N with an exotherm value of 29.3 J/g; IV (590−636 ℃): &lt;i&gt;γ&lt;/i&gt;'-Fe&lt;sub&gt;4&lt;/sub&gt;N→&lt;i&gt;γ&lt;/i&gt;-Fe with an exotherm value of 42.6 J/g; V (636−690 ℃): &lt;i&gt;γ&lt;/i&gt;-Fe→α-Fe with an endothermic value of 14.4 J/g. According to the phase transition law of Fe-N system, the crystal phase of iron nitride thin film is effectively regulated by vacuum annealing. The x-ray diffraction pattern (XRD) results show that the iron nitride thin film obtained by direct-sputtering in pure N&lt;sub&gt;2&lt;/sub&gt; is a single-phase &lt;i&gt;γ&lt;/i&gt;"-FeN film, and it becomes a single-phase ξ-Fe&lt;sub&gt;2&lt;/sub&gt;N film after being annealed at 350 ℃ for 2 h, a single-phase ε-Fe&lt;sub&gt;3&lt;/sub&gt;N film after being annealed at 380 ℃ for 2 h, and a single-phase &lt;i&gt;γ&lt;/i&gt;'-Fe&lt;sub&gt;4&lt;/sub&gt;N film after being annealed at 430 ℃ for 7 h. The annealing temperature for the phase transition of Fe-N thin film is generally lower than that predicted by the TG-DSC experimental results, because it is affected by the annealing time too, that is, prolonging the annealing time at a lower temperature is also effective for regulating the crystal phase of Fe-N thin film. The magnetic properties of the Fe-N thin film are also studied via vibrating sample magnetometer (VSM) at room temperature. The &lt;i&gt;γ&lt;/i&gt;'-Fe&lt;sub&gt;4&lt;/sub&gt;N polycrystalline thin film shows an easy-magnetized hysteresis loop for the isotropic in-plane one, but a hard-magnetized hysteresis loop with a large demagnetizing field for the out-of-plane one, which belongs to the typical magnetic shape anisotropy. However, their saturation magnetizations are really the same (about 950 emu/cm&lt;sup&gt;3&lt;/sup&gt;) both in the plane and out of the plane.

Grain Growth and Solid-State Dewetting of Bi-Crystal Ni-Fe Thin Films on Sapphire

We studied the solid-state dewetting behavior of thin Ni80Fe20 films deposited on basal plane oriented sapphire substrate and annealed in the range of temperatures of 1023-1323 K. All studied films exhibited strong texture and maze bicrystal microstructure, with only two grains misoriented by 60° around the common axis present in the film. The morphology of partially dewetted films changed from the one typical for polycrystalline thin films to the one typical for single crystalline heteroepitaxial films with increasing temperatures and annealing times. This change of dewetting behavior was associated with the fast grain growth in the films. The films of pure Ni of identical thickness, annealed under identical conditions exhibited significantly slower grain growth and lower thermal stability. Both the high-resolution X-ray diffraction and the cross-sectional high-resolution transmission electron microscopy observations revealed the phase separation of the Ni80Fe20 films into two parallel layers of the face-centered cubic (adjacent to the substrate) and hexagonal close-packed (on the top of the film) phases of similar compositions. Our density functional theory (DFT) calculations indicated that this phase separation is driven by the decrease of the film surface and interface energy, leading to the thermodynamically equilibrium thickness of the metastable hexagonal close-packed phase. This phase exhibits higher surface anisotropy than its stable face-centered cubic counterpart and is instrumental in accelerating the grain growth in the film via suppression of grain boundary grooving.

Design Optimization of an Anisotropic Magnetoresistance Sensor for Detection of Magnetic Nanoparticles

Recent studies have shown that the magnetic field sensitivity of an anisotropic magnetoresistance (AMR) sensor using a single-layer Ni80Fe20 thin film can be considerably improved by increasing the shape anisotropy of the film. In this work, an effective approach for improving the sensitivity and reducing the magnetic coercive field as well as the thermal noise contribution in an AMR Wheatstone bridge sensor is proposed by combining multiple resistors in the series–parallel combination circuits. Four different AMR sensor designs, consisting of a single resistor, three and five resistors in series and six resistors in series–parallel connection, were fabricated by using Ta (10 nm)/Ni80Fe20 (5 nm)/Ta (10 nm) films grown on thermally oxidized Si substrates under the presence and the absence of a biasing magnetic field (900 Oe). The results showed that the sensors based on series–parallel combination gain a magnetic sensitivity (SH) 1.72 times higher than that of the sensor based on the series connection. This optimized sensor has improved the capacity of detecting various concentrations of magnetic nanoparticles with a detection limit of magnetic moments estimated to be about 0.56 μemu.

Microwave Absorbance of Polymer Composites Containing SiC Fibers Coated with Ni-Fe Thin Films

Microwave Absorbance of Polymer Composites Containing SiC Fibers Coated with Ni-Fe Thin Films

Controllable synthesis of γ′-Fe4N via prolonged high vacuum magnetic annealing of deposited Fe–N thin films

Abstract In order to develop a fast and low-cost method for preparing γ′-Fe4N thin films for spintronic applications, the iron nitride (Fe–N) thin films were deposited through reactive sputtering in pure nitrogen, followed by high vacuum magnetic annealing process. The X-ray diffraction pattern (XRD) results revealed that the N content of the Fe–N thin films were decreasing continuously with the increase of annealing temperatures and times, so as to affect their crystal phase compositions, thus a single phase of γ″-FeN, ξ-Fe2N and γ′-Fe4N can be controllable prepared through annealing process. The phase transition characteristics for Fe–N to γ′-Fe4N were studied carefully. It was found that the sample (Fe1.8N) with a mixed crystal phase of γ″-FeN and ξ-Fe2N can be totally changed into a single phase of γ′-Fe4N by annealing it at 430 °C for 3 h, and the annealing temperatures can also be as low as 375 °C but for a prolonged time to 24 h. The stoichiometric matter of the as-prepared Fe–N thin films was confirmed by the XPS analysis. The vibrating sample magnetometer (VSM) results indicated that the magnetic properties of the Fe–N thin films are mainly depending on their crystal phase compositions. The saturation magnetization (Ms) of γ′-Fe4N films depends on various factors, and it was to about 1080 emu/cm3 for the γ′-Fe4N/MgO/Si.

Magnetic response of random lasing modes in a ZnO nanoparticle film deposited on a NiFe thin film

This study experimentally demonstrates lasing mode switching within a ZnO nanoparticle film coated onto a magnetic thin film of NiFe alloy. When a neodymium magnet is brought close to or moved away from the film, switching behavior is observed in the lasing modes, although such change is not induced in a ZnO nanoparticle film on a glass substrate. Our results suggest that the observed changes in lasing modes are because of a magneto-optical effect at the surface of the NiFe thin film. The magneto-optical effect would be enhanced by localized fields near the surface, inducing suppression or enhancement of the lasing modes in response to the surrounding environments, and accounting for the lasing mode switching.

Growth of epitaxial Fe0.5Ni0.5 thin films and their magnetic properties

Growth conditions for the epitaxial Fe0.5Ni0.5 (FeNi) thin films were optimized in order to enhance crystallinity and magnetism. Epitaxial thin films of FeNi (111) were successfully grown on (0001) Al2O3 substrates at substrate temperature of 400 °C. In addition, thickness dependence on structural and magnetic behavior of epitaxial FeNi thin films has been investigated using x-ray diffraction, x-ray reflectometry and vibrating sample magnetometer. The change in magnetization and coercivity are explained as a result of various anisotropic effects (stress, magneto-crystalline and shape anisotropies) as well as domain size in the FeNi film with a thickness range 195 Å to 703 Å. It is observed that, the magnetism is strongly dependent upon the microstructure and the thickness of the magnetic layer.