NiFe Films Research Articles

深共晶溶媒から作製した軟磁性膜の磁気特性や結晶組織に与える浴添加剤の影響

Deep eutectic solvents (DESs), a kind of ionic liquids, are expected as a novel solvent for electroplating due to their unique properties such as low vapor pressure, non-combustibility, high thermal stability, and high conductivity. We have employed DES as a solvent to obtain soft magnetic Fe-Ni films and have reported that glycine is an effective bath additive to reduce the coercivity in Fe-rich Fe-Ni films. In the present study, we employed boric acid as an additive in the plating bath and investigated the effect of boric acid on the magnetic and structural properties of Fe-Ni films. The addition of the boric acid reduced the coercivity of the Fe-Ni films. In particular, the boric acid dramatically reduced the coercivity in Fe-poor films, and this behavior was quite different from that for the glycine. From the result of the TEM observation, we confirmed that the Fe-Ni films with low coercivity had a fine crystal structure, which suggested that the fine structure supported improving the soft magnetic properties.

Fabrication of L10-ordered FeNi films by denitriding FeNiN(001) and FeNiN(110) films

Fabrication of L10-ordered FeNi films by denitriding FeNiN(001) and FeNiN(110) films

Magnetic domain-dependent ultrafast optical demagnetization in stripe domain films

We investigated femto- and picosecond-time magnetization dynamics in a ferromagnetic Ni80Fe20 film with varying thicknesses (wedge-shaped film). We observed that the thickness gradient strongly affects the magnetic moment distribution, causing a magnetization reorientation from in-plane to out-of-plane, and formatting a stripe domain (SD) at the thicker end of the wedge. The magnetization dynamics measurements reveal that the part of the film displaying SDs follows a substantially faster demagnetization and magnetization recovery and smaller magnetization quenching compared to the in-plane domain film. The experiments and micromagnetic simulations support that the decrease in relaxation time is caused by a magnetic anisotropy of the films introduced by SD formation. Our results point out that the micromagnetic structure plays an important role in the magnetization dynamics in ferromagnetic films after optically triggered demagnetization.

Improvement of some physical and magnetic properties of nanocrystalline Fe15–Ni85/ITO thin films by galvanostatic pretreatment process

In this research, a comparative study on some physical and magnetic properties of nanocrystalline Fe15–Ni85 thin films with and without galvanostatic pretreatment (GPT) process deposited on conductive and transparent indium tin oxide substrates using the electrodeposition method is carried out. The films exhibit the non-preferential deposition of more noble Ni. The films, irrespective of the GPT process, show a single face-centered cubic structure with the preferential orientation of crystallites along the (111) plane. The Ni-Fe thin film with the GPT exhibits a smaller crystallite size and a stronger [111] texture than the Ni-Fe thin film without the GPT. The films exhibit in-plane magnetic hysteresis loops with a magnetic squareness ratio of about 0.10 ± 0.01 independent of the GPT. The main advantages of the Ni-Fe thin film with the GPT are the smooth surface with smaller particles and the in-plane magnetization, which shows a significant reduction of the coercive field. The results obtained in this study are expected to be useful for future experimental studies of Ni-Fe thin film materials.

Estimation of Kerr angle based on weak measurement with two pointers.

In this paper, we propose a weak measurement method using two pointers to estimate the magneto-optical Kerr angle, which is robust to ellipticity. The double pointers are the amplified displacement shift and intensity of the post-selected light beam, which are the conventional information carried by the light beam and can be directly output by a detector (such as a charge-coupled device). We demonstrate that the product of the double pointers is only related to the phase variation between two basic vectors and independent of the amplitude errors. In the measurement process, when there is an amplitude change or additional amplitude noise between two eigenstates, the product of two pointers is very useful in extracting phase information and shielding amplitude noise. In addition, the product of two pointers has a good linear relationship with the phase variation and a larger dynamic measurement range. This method is applied to measure the magneto-optical Kerr angle of NiFe film. The Kerr angle can be directly obtained using the product of the light intensity and the amplified displacement shift. This scheme is of great significance for the measurement of the Kerr angle of magnetic films.

Rotatable anisotropy in exchange bias bilayer and stripe domains films with uniaxial anisotropy

We report the rotatable anisotropy in three magnetic film systems, including in-plane magnetized FeNi film, FeNi/FeMn bilayer and FeNi stripe domains (SDs) structure film. Omnidirectional ferromagnetic resonance driven by rotatable anisotropy can be achieved in these films. We have found that the in-plane magnetized FeNi films have a negligible rotatable anisotropy of about 1 ∼ 2 Oe. Rotatable anisotropy fields of 6.1 Oe and 5.5 Oe are found for isotropic and anisotropic FeNi/FeMn bilayers, which comes from the exchange coupling at the interface of FM and AFM layer. This magnitude is smaller than the value found in thick FeNi film where a big rotatable anisotropy field of 87 Oe is present stemming from its domain structure. In addition, the uniaxial anisotropy could tailor the resonance frequency from 0.78 and 2.28 GHz for in-plane magnetized FeNi thin film, and 1.3 to 2.4 GHz for FeNi SDs films. Furthermore, a conclusion that a uniaxial anisotropy has no influence on rotatable anisotropy in three magnetic films systems, was yielded.

Negative anisotropy in Ni–Fe films

Fe–Ni films were obtained in which the effect of “negative anisotropy” is observed. This effect consists in the formation of easy magnetization axis perpendicular to the deposition field. A model based on negative magnetostriction, and inhomogeneous stresses is tested. The model parameters were varied by applying additional stresses to the film. The effect of additional stresses is analyzed by changing the shape of the R–H curves. It is shown that changes in anisotropy occur in accordance with the model.

Application of electroplated Ni–Fe thick film to magnetostrictive material in vibration power generator

Ni100−xFex (at. %) films of about 37 μm thickness are electroplated on Cu base plates of 50 mm length, 10 mm width, and 300 μm thickness by varying the composition from x = 0 to 99. They are applied to cantilevers in magnetostrictive vibration power generators. The influences of magnetic and magnetostrictive properties of electroplated film on the vibration power generation property are systematically investigated. The films with x = 41–65 show low coercivities of about 4 Oe reflecting the low magnetocrystalline anisotropy constants. Large negative magnetostriction is recognized for the films with x = 0–14, whereas large positive magnetostriction is observed for the films with x = 57–80. The cantilevers are vibrated at the respective resonance frequencies of about 105–115 Hz and with the acceleration of 1.5 G while applying the bias magnetic field in a range of 0–300 Oe along the length direction. The output voltages are detected by using a coil with 8000 turns. Peak voltages higher than 1 V are obtained for the films with x = 61–65 whose coercivities are low and magnetostrictions are large. The present study has shown that an Ni–Fe film not only with large magnetostriction but also with low magnetic anisotropy constant is useful as the magnetostrictive material in vibration power generator.

Out-of-plane Ferromagnetic Resonance and Surface Spin Wave Modes in Ni80Fe20 Film on Ripple-Patterned Sapphire Substrate

The study of surface magnetic anisotropy of magnetic films is beneficial to understanding the behaviors of films at high frequencies and further promoting their high-frequency magnetic applications. We investigated the out-of-plane ferromagnetic resonance (FMR) and surface spin wave modes in 40-nm Ni80Fe20 (NiFe) films deposited on ripple-patterned sapphire substrate with periodicity and a flat sapphire substrate by broad-band FMR technique. When measuring the FMR of the film on ripple-patterned substrate, the in-plane angle (\U0001d711 H of the external applied magnetic field was along the direction of the ripples (\U0001d711 H = 90°) and perpendicular to the ripple direction (\U0001d711 H = 0°) respectively. The spin-wave resonance spectra consisting of up to two surface spin wave (SSW) modes were observed as the external magnetic field polar angle θH varied from “in-plane configuration” (θH = 90° ) to “out-of-plane configuration” (θH = 0°). As the decrease of θH , the two surface spin excitations disappeared in sequence and further only FMR mode was observed in the region θH which was smaller than the “critical angle” θc . The θc of \U0001d711 H = 90° is found to be different from that for \U0001d711 H = 0°. The dependences of field shift vs. out-of-plane angles θH for each SSW mode were analyzed by the surface inhomogeneity model. From the model, the surface anisotropy constants Ks of films were obtained. The results show that the values of surface anisotropy constants for the two SSW modes are different. Compared with the film sputtered on flat sapphire substrate, after introducing ripple-patterned substrate, the variation of Ks is only on the order of 0.01 erg/cm2 for the film of this thickness.

Exchange stiffness constant determination using multiple-mode FMR perpendicular standing spin waves

The exchange stiffness constant is recognized as one of the fundamental properties of magnetic materials, though its accurate experimental determination remains a particular challenge. In thin films, resonance measurements exploiting perpendicular standing spin waves (PSSWs) are increasingly used to extract this parameter, typically through a determination of the first-order PSSW mode. Here, we present a systematic study of multiple PSSW modes in NiFe films, where both the sample thickness and the cap layer material are varied. The results show that a simple analysis based on the Kittel rigid pinning model yields an exchange stiffness constant that varies with thickness, mode number, and capping layer material. This finding is clearly inconsistent with physical expectation that the exchange stiffness constant of a material is single valued for a particular set of thermodynamic conditions. Using a more general exchange boundary condition, we show, through a comprehensive set of micromagnetic simulations, that a dynamic pinning mechanism originally proposed by Wigen is able to reproduce the experimental results using a single value of Aex. Our findings support the utility of short wavelength, higher order PSSWs to determine the Aex of thin films and show that the value of Aex obtained has a weak dependency on the material immediately adjacent to the magnetic layer.

Micromorphology and uniaxial magnetic anisotropy of oblique-sputtered Ni80Fe20 films on periodically rippled Al2O3 substrates

Ni80Fe20 (NiFe) films were deposited on periodically rippled Al2O3 substrates by two different template oblique angle deposition (OAD) processes at various oblique deposition angles α (0° ≤ α ≤ 60°). The disparate in-plane uniaxial magnetic anisotropy (UMA) caused by the two template deposition processes of films was revealed by magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) measurements. The analysis of Transmission electron microscopy images indicated that this was related to the different micromorphology of the films due to the two template deposition processes. The angle between substrates’ ripple direction and the material flow incident direction would strongly influence the micromorphology and the induced in-plane UMA field of films. The values of the UMA field of these films can be much larger than those of the films oblique deposited on the plane Al2O3 substrates at the same α by choosing the template deposition direction. The results would help further modulate the UMA of magnetic films deposited on rippled substrates, which would be beneficial for the applications of these films in spintronic, magnetic memory and magnetic microwave devices.

Magnetoimpedance effect in electrodeposited NiFe/Cu wire using trisodium citrate additive in plating bath

Magnetoimpedance (MI) and magnetic properties of the electroplated NiFe/Cu thin films with a steadily rising concentration of trisodium citrate (TSC) additive in the plating bath is systematically examined in a wide frequency range of 10 kHz–8 MHz. The addition of TSC to the plating bath reduces the crystalline size and coercivity of the NiFe film, resulting in increased magnetic softness and MI ratio. The grain refining action of TSC additive is responsible for the random distribution of magnetic anisotropy axis in individual tiny crystallite which enhance circumferential permeability of deposited film and its MI ratio. The optimum concentration of TSC additive is found to be 40 g/l and sample electrodeposited at that TSC concentration boosts the MI ratio to 113% as compared to 28% when no TSC is used. When the film is deposited without any additive, a typical double peak behavior of the MI response curve is exhibited at higher frequency. This feature is eradicated with slightest inclusion of TSC additive in the electrodeposition bath which is an indication that inclusion of trisodium citrate weakens the circumferential anisotropy in plated film. Based on the analytical formulation of circumferential permeability the results of MI measurements are mapped with the theoretical framework, and the circumferential permeability of the NiFe magnetic film is reconstructed by curve fitting. Through the investigation of the fitting parameters, it is found that the addition of TSC to the bath completely annihilates the circumferential anisotropy found in as deposited permalloy film which is responsible for the transition from double to single peak behavior of MI response at higher frequencies.

Soft magnetic Fe–Ni thick films plated on a non-conductive substrate using an electroless plating

We prepared Fe–Ni films on non-conductive substrates (Polyimide sheets) using the electroless plating method and investigated the metallization process of the PI sheets and the magnetic properties of the films. To obtain suitable conditions for the metallization of the PI surface, we changed the immersion time in KOH and AgNO3. As a result, the thickness slightly increased with increasing the immersion time in KOH, and the obvious effect of the immersion time in AgNO3 on the film thickness was not observed. The coercivity of the films plated on the PI sheet increased with increasing the thickness due to an increase in the roughness, and the value of coercivity was almost the same as previously reported ones (Hc = 30–96 A/m) using conductive substrates. We, therefore, concluded that the Fe–Ni films with low coercivity could be obtained by the optical metallization of the PI surface.

Особенности плоскостной магнитной анизотропии и доменной структуры пленок FeNi, осажденных в присутствии магнитного поля различной конфигурации

FeNi films in circular shape with 3 mm in diameter obtained by magnetron sputtering in the presence of a constant magnetic field of various configurations are studied. The presence of a field created by a permanent magnet with a diameter of 1.2 mm, the magnetization of which is oriented perpendicular to the plane of the substrate, leads to the formation of a vortex-like magnetic structure in the film, characterized by diffuse domain walls.

In-plane magnetic anisotropy and domain structure of FeNi films deposited in the presence of a magnetic field of various configurations

FeNi films in circular shape with 3 mm in diameter obtained by magnetron sputtering in the presence of a constant magnetic field of various configurations are studied. The presence of a field created by a permanent magnet with a diameter of 1.2 mm, the magnetization of which is oriented perpendicular to the plane of the substrate, leads to the formation of a vortex-like magnetic structure in the film, characterized by diffuse domain walls. Keywords: thin magnetic films, induced magnetic anisotropy, magnetic domain structure, magnetron sputtering.

Control of N atom content in Fe-Fe<sub>3</sub>N film with high saturation magnetization and low conductivity

Microelectronic devices have a wide range of application prospects. In order to make microelectronic devices that have excellent high-frequency characteristics, developing of soft magnetic films with high saturation magnetization, low coercivity and high resistivity becomes the key to the research. In this work, Fe-Fe<sub>3</sub>N soft magnetic films with different numbers of N atoms are prepared by radio-frequency atomic source assisted vacuum thermal evaporation. Among them, the RF atom source provides N atoms with higher chemical activity than N molecules, which reduces the formation energy between Fe atoms and N atoms. The vacuum thermal evaporation is beneficial to accurately controlling the growth rate, impurity concentration and composition ratio of multiple compounds of the film at the atomic level. The combination of the two Fe aom and N atom is easier to form nitrides with Fe atoms. Thus in this way the Fe-N films with stable structure are obtained. In the prepared Fe-Fe<sub>3</sub>N soft magnetic film, the introduction of N atoms makes the surface of the film more uniform, resulting in the increase of density. Compared with Fe, surface roughness is reduced by two times, and the crystallinity is obviously enhanced. Owing to the high saturation magnetization, the content of Fe<sub>3</sub>N phase is increased by 29% and the (102) orientation of Fe<sub>3</sub>N increases to 0.64. Therefore the directionality of the magnetic moment arrangement is improved. Comparing with Fe film, the saturation magnetization of the film is increased by 55.2%, reaching 1705.6 emu/cm<sup>3</sup>. In addition, with the increase of the (102) orientation of Fe<sub>3</sub>N, a large number of lattice mismatches are produced, which impedes the growth of Fe and Fe<sub>3</sub>N grains and reduces the grain size and anisotropy of the film. Thus the coercivity of the film decreases. The coercivity (50.3 Oe) is 68.6% lower than that of the Fe film. At the same time, the larger lattice mismatch results in the increase of heterointerface, which promotes the carrier scattering and increases the resistivity of Fe-Fe<sub>3</sub>N thin film. The resistivity (8.80 μΩ·m) of Fe-Fe<sub>3</sub>N thin film is 7 times higher than that of Fe thin film. Therefore, this research provides a new method for studying and developing soft magnetic films with high saturation magnetization, low coercivity and high resistivity.

Congruent Electrochemical Deposition of Co–Ni–Fe Films

Congruent Electrochemical Deposition of Co–Ni–Fe Films

Mechanical Stresses and Magnetic Properties of NiFe and CoNiFe Films Obtained by Electrochemical Deposition

Mechanical Stresses and Magnetic Properties of NiFe and CoNiFe Films Obtained by Electrochemical Deposition

Structural and Magnetic Properties of FeNi Films and FeNi-Based Trilayers with Out-of-Plane Magnetization Component

FeNi films of different thickness and FeNi/(Fe, Co)/FeNi trilayers were prepared by magnetron sputtering deposition onto glass substrates. The permalloy films had a columnar microstructure. The detailed analysis of the magnetic properties based on the magnetic and magneto-optical measurements showed that at thicknesses exceeding a certain critical thickness, hysteresis loops acquire a specific shape and the coercive force of the films increase sharply. The possibility of the estimation of the perpendicular magnetic anisotropy constant using the Murayama equation for the thickness dependence of saturation field was demonstrated. The results of studies of the structural and magnetic properties of FeNi films laminated by Fe and Co spacers with different thickness are presented.

The Effect of Obliquely Sputtered Cu Underlayers with Different Thicknesses on the Magnetic Properties of 50 nm Ni80Fe20 Thin Films

The magnetic properties of 50 nm Ni80Fe20 deposited on Cu underlayers with different thicknesses by obliquely sputtering were studied. It was found that the in-plane uniaxial magnetic anisotropy (IPUMA) of the Ni80Fe20 film can be induced by the obliquely sputtered Cu underlayer deposited under the NiFe layer. The IPUMA field of NiFe film varies between 20 Oe and 40 Oe when the thickness of Cu underlayer varies from 5 nm to 50 nm. The permeability spectrum results show that the damping factor increases with increasing Cu underlayer thickness. This indicates that changing the thickness of the Cu underlayer of obliquely sputtering is an effective method to adjust the damping factor in the dynamic magnetization process of Ni80Fe20 thin films.