Soft Magnetic Films Research Articles

Exchange coupled L10 FeCuPt/Fe heterostructures: Magnetic properties and reversal behavior at elevated temperatures

Exchange-coupled heterostructures were prepared by combining hard magnetic L10 FeCuPt alloy films with soft magnetic Fe thin films. For the FeCuPt thin film, the addition of Cu allows adjusting magnetic properties such as perpendicular magnetic anisotropy, coercivity, saturation magnetization, and Curie temperature. The coupling to thin Fe layers, providing high saturation magnetization and high Curie temperature, leads to lowering of the switching field of the hard magnetic FeCuPt layer and to a reduction of thermally induced recording errors. We have investigated the influence of the Fe layer thickness on the switching behavior of the hard layer, revealing a strong reduction for Fe layer thicknesses larger than the exchange length of Fe of about 2nm. Furthermore, superior performance of bilayer structures in comparison to single FeCuPt layers has been demonstrated by recording experiments at temperatures below 150°C, employing a scanning magnetoresistive microscope.

Enhancement of in-plane uniaxial magnetic anisotropy for patterned nanoparticle films fabricated by electric field-assisted deposition

The patterned FeNi nanoparticle films with strip width 60µm were prepared by electric field-assisted deposition technique. Application of electric field drove the accelerating deposition of the condensed nanoparticles, promoting the formation of the films with high stacking density. Besides the excellent soft magnetic characteristics, the samples showed an obvious enhancement of in-plane uniaxial magnetic anisotropy when they were annealed in vacuum environment at proper temperatures. The increase of in-plane uniaxial magnetic anisotropy, which is due to the release of stress with increasing temperature, is also confirmed by scanning microwave permeability spectra in GHz range. The experimental results imply that optimization of in-plane uniaxial magnetic anisotropy is particularly attractive for the application of electric field deposited soft magnetic nanoparticle films in the high-temperature processing electromagnetic devices.

Improvement of microwave permeability spectra in high stacking density FeNi nanoparticle films prepared by electric field-assisted deposition

We proposed an advanced method to improve saturation magnetization of soft magnetic nanoparticle films, which are of great concern for application in modern electromagnetic devices operated in the GHz range. Fe50Ni50 nanoparticle films with a particle size of about 6 nm were fabricated at room temperature by electric field-assisted deposition. An electric field of 10–20 kV was applied on the deposition platform during the film’s manufacture to obtain high stacking density and superior in-plane soft magnetic properties in the films. Based on the results of the microwave permeability spectra, it is found that the samples with higher saturation magnetization have excellent microwave response. These results indicate that magnetic softness and microwave behavior of FeNi nanoparticle films can be modulated by applying electric field during deposition.

Simulation of M–H Loops in FeCo Polycrystalline Thin Films at Finite Temperatures**Supported by the National Natural Science Foundation of China under Grant Nos 51171086 and 51371101.

We apply the hybrid Monte Carlo (HMC) micromagnetic method to FeCo soft magnetic polycrystalline films and test the new method by comparing with the result worked out by micromagnetics using Landau–Lifshitz–Gilbert equations, and the magnetic properties of FeCo films are understood better by carefully considering the effects of polycrystalline microstructures. The hysteresis loops of the FeCo film from low temperature up to 1100 K are simulated by the new HMC micromagnetic method.

Achievement of Diverse Domain Structures in Soft Magnetic Thin Film through Adjusting Intrinsic Magnetocrystalline Anisotropy

Oriented soft magnetic hcp-Co1 − xIrx films with a fixed thickness of 120 nm were fabricated. All prepared films exhibit soft magnetic properties but various magnetocrystalline anisotropies with the variation of Ir content. The measured data shows that diverse domain structures including the Néel wall, Bloch wall, and stripe domains present in a fixed film thickness. It is singular for the single-layer soft magnetic film to possess diverse domains in a fixed thickness. This phenomenon was explained by introducing intrinsic magnetocrystalline anisotropy energy into soft magnetic films rather than the structural parameters of the film, inner stress, and microstructure effect.

A tunable broadband magnetoelectric and electromagnetic hybrid vibration energy harvester based on nanocrystalline soft magnetic film

In this paper, a tunable broadband electromagnetic (EM) and magnetoelectric (ME) hybrid vibration energy harvester (HVEH) employing a hybrid transducer and double cantilever to convert low-frequency vibration energy into electrical energy is presented. The electric output performances of the proposed HVEH have been investigated. Compared to single ME or EM vibration energy harvester (VEH), the experiment results show that the proposed HVEH can simultaneously obtain an enhanced output performance including higher power, voltage, current and wide bandwidth. It is found that the output power and resonance frequency of HVEH can be tuned by controlling the FeCuNbSiB layer thickness, turns number and cantilever length, respectively. When FeCuNbSiB layer thickness, cantilever length and turns number is 30μm, 5cm and 750, the optimum output power and effective bandwidth of HVEH achieve 36.8mW and 5.6Hz for an acceleration of 0.75g at frequency of 32Hz, respectively. Remarkably, the proposed HVEH has great potential for its application in wireless sensor networks.

Method for nanomodulation of metallic thin films following the replica-antireplica process based on porous alumina membranes

In this paper we have introduced a method for modulation of metallic thin films by sputtering of metals on anodized aluminum templates. Using a high deposition rate during deposition of the non-magnetic metal on the Al pattern, we have separated the two metallic surfaces and, thus, imprinted a pattern of nanohills on a non-magnetic metallic film, such as Au, Ag or Cu. The morphology of the nanostructured metallic films was determined by scanning electron microscopy. Thus, we have confirmed that the ordering degree of the Al template remained after the replication process. Additionally, and as an example of use of these films, we have prepared Supermalloy thin films deposited by sputtering onto these nanostructured non-magnetic metals. The room temperature magnetic behavior of these thin films is also studied. Interestingly, we have found that when the external magnetic field is applied out of plane of the substrate, the coercivity increases linearly as we increase the radius of the nanohills. These soft magnetic films can open new opportunities for magnetic field sensor applications.

Magnetic Multilayer Fabrication Technology with Selective Activation of SU-8 Films

Developing magnetic multilayers are essential for reducing the core eddy current losses in the integrated power magnetic components (inductors/transformers). PVD based processes are typically used to achieve the multilayers with thin dielectric spacers. However, those processes are costly, and can be difficult to integrate. It is evident that cost effective alternative is needed. In recent years, electrochemical processes have been investigated to address these issues. One such method would be to successive metallization of insulating photoresists acting as spacer layer (such as SU-8) with soft magnetic films (such as Ni-Fe-Co alloys). This paper describes an experimental procedure to fabricate magnetic multilayers with a thin variant of SU-8 2 (<1.5 μm) as inter-layers for integrated micro-inductors/transformers for power conversion applications.

Engineering optical mode ferromagnetic resonance in FeCoB films with ultrathin Ru insertion.

Ferromagnetic resonance (FMR) in soft magnetic films (SMFs) to a large extent determines the maximum working frequency of magnetic devices. The FMR frequency (fr) in an optical mode is usually much higher than that in the corresponding acoustic mode for exchange coupled ferromagnet/nonmagnet/ferromagnet (FM/NM/FM) trilayers. In this study, we prepared a 50 nm FeCoB film with uniaxial magnetic anisotropy (UMA), showing a high acoustic mode fr of 4.17 GHz. When an ultrathin Ru spacer was inserted in the very middle of the UMA-FeCoB film, the zero-field FMR was abruptly switched from an acoustic mode to an optical one with fr dramatically enhanced from 4.17 GHz to 11.32 GHz. Furthermore, the FMR mode can be readily tuned to optical mode only, acoustic mode only, or double mode by simply varying the applied filed, which provides a flexible way to design multi-band microwave devices.

Patterned FeNi soft magnetic strips film with tunable resonance frequency from 1 to 10.6 GHz.

Soft magnetic films with a wide-range tunable ferromagnetic resonance frequency are suitable for miniaturization and multifunctionalization of microwave integrated circuits. Fabrication of these films for high-frequency applications is usually complicated and difficult. We demonstrate a simple method to fabricate patterned FeNi soft magnetic strip films by magnetron sputtering and photolithography. Films prepared by this method exhibits a tunable in-plane uniaxial magnetic anisotropy (IPUMA) for different strip widths and gaps. As the strip widths changing from 500 to 2 μm, the IPUMA field increases monotonically from 2.2 to 576 Oe and resonance frequency from 1 to 10.6 GHz(which covers four microwave bands, including the L,S,C and X bands) respectively. This ultra-wide-range adjustability of resonance frequency can be attributed to shape anisotropy of strips. Considering that FeNi alloy has relatively low magnetocrystalline anisotropy, so a wider adjustable range of resonance frequency could be obtained using materials with stronger magnetocrystalline anisotropy.

Phase separation in NiCrN coatings induced by N2 addition in the gas phase: A way to generate magnetic thin films by reactive sputtering of a non-magnetic NiCr target

Magnetic coatings are used for a lot of applications from data storage in hard discs, spintronics and sensors. Meanwhile, magnetron sputtering is a process largely used in industry for the deposition of thin films. Unfortunately, deposition of magnetic coatings by magnetron sputtering is a difficult task due to the screening effect of the magnetic target lowering the magnetic field strength of the magnet positioned below the target, which is used to generate and trap ions in the vicinity of the target surface to be sputtered. In this work we present an efficient method to obtain soft magnetic thin films by reactive sputtering of a non-magnetic target. The aim is to recover the magnetic properties of Ni after dealloying of Ni and Cr due to the selective reactivity of Cr with the reactive nitrogen species generated during the deposition process.The effects of nitrogen content on the dealloying and DC magnetron sputtering (DCMS) deposition processes are studied here. The different chemical compositions, microstructures and magnetic properties of DCMS thin films obtained by sputtering in reactive gas mixtures with different ratios of Ar/N2 from a non-magnetic Ni-20Cr target have been determined. XPS data indicate that the increase of nitrogen content in the films has a strong influence on the NiCr phase decomposition into Ni and CrN, leading to ferromagnetic coatings due to the Ni phase. XRD results show that the obtained Ni-CrN films consist of a metallic fcc cubic Ni phase mixed with fcc cubic CrN. The lattice parameter decreases with the N2 content and reaches the theoretical value of the pure fcc-Ni, when Cr is mostly removed from the Ni-Cr phase. Dealloying of Cr from a Ni80-Cr20 solid solution is achieved in our experimental conditions and the deposition of Ni ferromagnetic coatings embedding CrN from a non-magnetic target is possible with reactive DC magnetron sputtering.

A model for asymmetric magnetoimpedance effect in multilayered bimagnetic films

The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The structure consists of the soft and hard magnetic films separated by highly conductive non-magnetic layer. A model to describe the magnetoimpedance effect in the film structure based on a simultaneous solution of linearized Maxwell equations and Landau–Lifshitz equation is proposed. It is shown that magnetostatic coupling between the magnetic layers results in the asymmetry in the field dependence of the film impedance. The magnetostatic coupling is described in terms of an effective bias field appearing in the soft magnetic layer. The calculated field and frequency dependences of the film impedance are shown to be in a qualitative agreement with previous results of experimental studies of the asymmetric magnetoimpedance in NiFe/Cu/Co film structures. The results obtained may be useful for development of weak magnetic-field sensors.

Centimeter-order view for magnetic domain imaging with local magnetization direction by longitudinal Kerr effect

An observation system of centimeter-order of view of magnetic domain with local magnetization direction was developed by designing a telecentric optical system of finite design through the extension of microscope technology. The field of view realized in the developed system was 1.40 × 1.05 cm as suppressing defocus and distortion. Detection of the local magnetization direction has become possible by longitudinal Kerr observation from the orthogonal two directions. This system can be applied to the domain observation of rough surface samples and time resolved analysis for soft magnetic materials such as amorphous foil strips and soft magnetic thin films.

Electroplated Fe-Co-Ni films prepared from deep-eutectic-solvent-based plating baths

We fabricated soft magnetic films from DES-based plating baths, and investigated magnetic properties of the plated films. The plating baths were obtained by stirring the mixture of choline chloride, ethylene glycol, FeCl2 ⋅ 4H2O, NiCl2 ⋅ 6H2O and CoCl2 ⋅ 6H2O. The composition of the electroplated film depended on the amount of the reagent in the plating bath, and we consequently obtained the films with various composition. The current efficiency of the plating process shows high values (&amp;gt; 88 %) in the wide composition range. The soft magnetic films with low coercivity were obtained at the Fe compositions of ≈ 30 at.% and &amp;gt; 80 at.%, and we found that low coercivity could be realized by the control of the film composition. We also found that the Fe-rich films prepared from DES-based plating bath have some advantages as a soft magnetic phase for a nanocomposite magnet due to their high saturation magnetization and very fine crystal structure.

Magnetic properties and high frequency characteristics of FeCoN thin films

(Fe65Co35)N soft magnetic thin films were prepared by reactive RF magnetron sputtering with the sputtering power of 100 W on thermally oxidized Si substrate in various nitrogen partial pressures (PN2). A strong uniaxial in-plane magnetic anisotropy with the easy-axis coercive field as low as 1∼2 Oe was observed in films grown at PN2 in the range from 3.3% to 5.5%. The saturation magnetizations for those films were about 20 KG. Outside this range, almost isotropic magnetization curves were observed. Vector network analyzer and grounded coplanar waveguide were used to measure the ferromagnetic resonance (FMR) signals up to 25 GHz. The FMR signals were detected only in anisotropic films and their FMR frequencies were well fit to the Kittel formula. The obtained g-values and damping parameters at magnetic fields &amp;gt;20 kOe for films grown at PN2 of 3.3%, 4.8% and 5.5% were 1.96, 1.86, 1.92 and 0.0055, 0.0047, 0.0046, respectively. This low damping factor qualifies FeCoN thin films for high-frequency applications.

Three-dimensional simulation of irregular dynamics of topological solitons in moving magnetic domain walls

A three-dimensional computer simulation of dynamic processes occurring in a domain wall moving in a soft-magnetic uniaxial film with in-plane anisotropy has been performed based on the micromagnetic approach. It has been shown that the domain wall motion is accompanied by topological transformations of the magnetization distribution, or, more specifically, by “fast” processes associated with the creation and annihilation of vortices, antivortices, and singular (Bloch) points. The method used for visualizing the topological structure of magnetization distributions is based on the numerical determination of topological charges of two types by means of the integration over the contours and surfaces with variable geometry. The obtained data indicate that the choice of the initial configuration predetermines the dynamic scenario of topological transformations.

Adjustable high-frequency magnetic properties of oriented Co80Ir20 soft magnetic thin films with strong negative magnetocrystalline anisotropy

The oriented Co80Ir20 soft magnetic thin films with adjustable in-plane uniaxial anisotropy field and strong negative magnetocrystalline anisotropy ( $$K_{\text{u}}^{\text{grain}}$$ ) were fabricated by magnetron sputtering. The oblique angle dependence of the static and high-frequency properties for the oriented Co80Ir20 soft magnetic films was systematically investigated. The results suggest that the in-plane uniaxial anisotropy field (H u) can be adjusted by changing the oblique angle, while the total out-of-plane anisotropy field remains invariable. With the increase in the oblique angle, the value of H u varies from 80 to 310 Oe. As a result, the natural resonance frequency (f r) significantly increases from 4.6 to 7.9 GHz.

Hysteretic Behavior of the Dynamic Permeability in FeCoB Thin Films

The microwave permeability in a soft magnetic FeCoB film as a function of the external magnetic field is measured in the frequency range from 0.2 to 8 GHz. When the field applied parallel to the orientation of the magnetization varies from 90 to −90 Oe, the permeability spectrum shows hysteretic behavior. Double magnetic resonance peaks come forth and evolve in the imaginary part of the permeability when the field approaches the coercive field of the sample. This phenomenon is attributed to the formation of domains, the resonance frequency of the reversed domains being different than that of the non-reversed domains. Both peak frequencies and peak amplitudes are interpreted quantitatively using simple considerations based on the Landau–Lifshitz equation and the knowledge of the static magnetic properties of the film. The ratio of the reversed magnetic moments to the non-reversed ones is estimated by fitting curves of the permeability spectrum.

Enhanced film thickness for Néel wall in soft magnetic film by introducing strong magnetocrystalline anisotropy.

This study investigated the magnetic domain walls in a single-layer soft magnetic film with strong magnetocrystalline anisotropy energy. The soft magnetic film is composed of a highly c-axis-oriented hcp-Co81Ir19 alloy with strong negative magnetocrystalline anisotropy. The domain structure of the soft Co81Ir19 films with thickness ranging from 50–230 nm in a demagnetization state was observed through magnetic force microscopy and Lorentz transmission electron microscopy. Results reveal that the critical transition thickness at which the domain wall changes from Néel type to Bloch type is about 138 nm, which is much larger than the critical value of traditional Fe- and Co-based soft magnetic films with negligible magnetocrystalline anisotropy. Theoretical calculation was also performed and the calculated result agrees well with experimental data.

The dependence of electromagnetic noise suppress characteristics on magnetic and high-frequency properties of FeCoSiO thin films

A series of soft magnetic granular FeCoSiO films is fabricated using radio frequency magnetron sputtering under pure argon ambient conditions. The magnetic, high-frequency, and microwave noise suppression characteristics of these thin films are studied in detail. By using microwave probe station, integrated-type electromagnetic noise suppressors based on a coplanar waveguide transmission line and incorporated with a SiO2 dielectric and a granular FeCoSiO magnetic thin film with excellent high frequency and soft magnetic properties are investigated. The relationship between transmission properties of electromagnetic noise suppressors and magnetic characteristics of FeCoSiO magnetic thin films were studied. The experimental values of the loss peak frequencies agree well with the calculated ferromagnetic resonant frequency, which considers the demagnetizing field. The results indicate that the main loss mechanism of the integrated devices is the ferromagnetic resonance, but not the L–C resonance. The FeCoSiO magnetic films are considered to be promising as ideal candidate materials for electromagnetic noise suppressor.