Soft Magnetic Characteristics Research Articles

High-temperature magnetic behavior of soft/soft and soft/hard Fe and Co-based biphase microwires

The magnetic behavior of biphase magnetic microwires has been investigated in the high-temperature range from 295 to 1200 K. Bimagnetic microwires consist of a magnetically soft amorphous core (i.e., positive, FeSiB, and negative, CoFeSiB, magnetostriction alloy) and external polycrystalline shell with soft (FeNi, Permalloy) and medium-hard (CoNi) magnetic character. The magnetic phase transitions (ferro to paramagnetic) of individual phases are first detected through the temperature dependence of magnetization where structural changes in the amorphous alloy cores are also identified. Moreover, the values of coercive field of individual and bimagnetic phase systems are analyzed in view of these magnetic and structural transitions. The study is relevant for technological applications of bimagnetic microwires in the temperature regime above room temperature.

Uniaxial in-plane magnetization of iron nanolayers grown within an amorphous matrix

Conversion electron Mössbauer spectroscopy is used to determine the magnetic ground state at zero magnetic field of four-monolayer thick amorphous iron layers as part of a CoFeB-Fe multilayer stack. By comparing the intensities of the magnetic hyperfine field, an easy in-plane axis of the amorphous embedded Fe layer is verified, which is collinear to the uniaxial anisotropy axis of the neighboring amorphous CoFeB. Despite the soft magnetic character of the Fe layers, external fields up to 4 T perpendicular to the film plane are insufficient to completely align the embedded Fe moments parallel to the magnetic field due to a local disorder of the magnetic moments of the Fe atoms.

Oriented hexagonal ferrite thin films prepared by chemical solution deposition

Hexagonal ferrites (M, Y, Z-type) represent a new diverse class of magnetoelectric (ME) multiferroics, where ME effect is driven by complex magnetic order. Integration of ME materials with standard semiconductor technology is important for ultimate realization of ME functionalities. They have the potential to display ME coupling under low magnetic field bias and at temperatures close to room temperature. Methods based on sol–gel transition offer possibility of low cost and efficient way for the evaluation of new material system. The single phase, epitaxial thin films of Y-type hexagonal ferrite has been prepared and studied. Thin films of Ba2Zn2Fe12O22(Y) hexaferrite were prepared through the chemical solution deposition method on SrTiO3(111)(ST) single crystal substrates using epitaxial SrFe12O19(M) hexaferrite thin layer as a seed template layer. The process of crystallization was mainly investigated by means of X-ray diffraction and atomic force microscopy. A detailed inspection revealed that growth of seed layer starts through the break-up of initially continuous film into high density of well-oriented isolated grains with expressive shape anisotropy and hexagonal habit.The vital parameters of the seed layer, i.e. thickness, substrate coverage,crystallization conditions and temperature ramp were optimized with the aim to obtain epitaxially crystallized Y phase. By overcoating this seed layer, Y phase prepared under optimum deposition and heat treatment conditions presents a (001) orientation perpendicular to the substrate. Perfect parallel in-plane alignment of the hexagonal cells of SrTiO3substrate and both hexaferrite phases was proved by fast ω and φ scan measurements on sets of several diffraction planes at asymmetric orientations, and also by pole figures. The soft magnetic character and existence of pronounced magnetic anisotropy in Y films were confirmed by room temperature measurements of magnetization.

Electrodeposition of Ag-Ni-Fe Nanowires

Present work provides an electrodeposition based methodology for synthesizing Ag-Ni-Fe nanowires. Nanowire morphology was achieved by using an anodic alumina membrane having cylindrical pores of similar to 200 nm diameter. Compositional analysis at a single nanowire level revealed a fairly uniform distribution of component elements in the nanowire volume. Structural characterization strongly indicated toward a presence of randomly oriented, non-equilibrium, nano-crystalline phase volume inside the nanowires. Magnetic characterization revealed a soft magnetic character for the as-synthesized Ag-Ni-Fe nanowires. (C) 2014 The Electrochemical Society. All rights reserved.

Essence of superparamagnetism in cadmium ferrite induced by various organic fuels via novel solution combustion method

An attempt has been made to enumerate the myriads of successful applications of magnetic materials in nano-regime via low-temperature solution combustion synthesis of cadmium ferrite using different organic fuels such as urea, oxalyl dihydrazide (ODH), glycine and ethylene glycol giving rise to 1D nanorods and monodispersed spherical nanoparticles, thereby exploring their applicability in nanoelectronic devices such as high speed integrated circuits as well as in biomedical field as contrasting agents used in magnetic resonance imaging (MRI) with enhanced magnetization. Thus, with appropriate selection of organic fuel and precursors (metal nitrates), single phase, cubic structured cadmium ferrites have been synthesized as depicted from FTIR spectroscopy and XRD patterns with particle size lying in 12–27nm regime as rendered from TEM micrographs. Magnetic studies in the shadow of Mössbauer studies prelude to the emergence of superparamagnetism with non-saturation of M–H loop and negligibly small values of remanence as well as coercivity at room temperature, hence attributing to its single domain as well as soft magnetic character. Moreover, the room temperature dielectric measurements show dispersion behavior with increasing frequency corresponding to low dielectric losses, hence making them suitable for applications in high-frequency devices. Thus, solution combustion methodology was successfully used as a key step in the synthesis of CdFe2O4 with highly superparamagnetic and soft character, thereby leading to products with different morphologies in nano-regime.

Fabrication and tuning soft magnetic and magneto-optical properties of BMGs based Fe-B-Nb-Ni transparent thin films, obtained by Pulsed Laser Deposition.

ABSTRACTWe have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200 oC); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/µm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.

Rapidly solidified Nd7Fe67B22Mo3Zr1 nanocomposite permanent magnets

Nd7Fe67B22Mo3Zr1 magnets in rods have been prepared by annealing the amorphous precursors produced through injection casting. Phase formation, microstructure and magnetic properties of Nd7Fe67B22Mo3Zr1 magnets have been investigated and discussed in the as-cast and annealed states. Cast Nd7Fe67B22Mo3Zr1 rods have the soft magnetic characteristics, which changed into magnetically hard by annealing. Magnetic properties in Nd7Fe67B22Mo3Zr1 magnets are influenced by the intrinsic properties of magnetically soft α-Fe (Fe3B) and hard Nd2Fe14B phases. The Zr and Mo elements in the Nd7Fe67B22Mo3Zr1 alloy promote the formation of amorphous phase and reduce the grain size of magnetic phases. Optimal annealed Nd7Fe67B22Mo3Zr1 rods of 2mm in diameter and 52mm in length presented maximum magnetic properties such as: remanence (Br) of 0.53T, coercivity (iHc) of 1110kA/m and maximum energy product (BH)max of 49.5kJ/m3.

Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

• Fe films have been grown on Si(0 0 1) substrates and subsequently hydrogenated. • As deposited films present soft magnetic character and a strong magnetic texture. • Structural and magnetic properties can be tuned via hydrogenation treatments. • Ferromagnetic/semiconductor interfaces might be manipulated via hydrogenation. In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(0 0 1) substrates by RF sputtering have been investigated using 57 Fe conversion electron Mössbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing.

Characterization of Nano-Sized SiC@Ni Composite Fabricated by Electroless Plating Method

A nano-sized SiC@Ni composite was prepared by simple electroless plating method. Nickel can be reduced by Na2H2PO2 under the catalysis of Pd to despite onto the surface of SiC nanoparticles. The composite structure was characterized by means of TEM images, XRD and the components were analyzed using EDS. The coating layer on the SiC particles was several nanometers thick and mainly in a form of fine Ni crystalline grain and amorphous Ni-P alloy. By increasing the concentration of Na2H2PO2 in the plating bath, the uniformity of the coating layer can be improved obviously. Both of the magnetism and crystallinity of Ni coatings depends on the P content in the coating which can be decreased by increasing the pH values of plating solutions. The SiC@Ni particles exhibited soft magnetic characteristics.

Recent Research on the Magnetoimpedance Effect in Co-Based Amorphous Ribbons

We report the recent results obtained on the magnetoimpedance (MI) response in several near-zero magnetostriction Co-based amorphous ribbons with different width, and different transverse magnetic anisotropy (developed during the fabrication process or processing after production by the current annealing technique) in the frequency range of 10 MHz – 3.5 GHz. The evolution of the maximum of MI with the axial magnetic field, ascribed to the anisotropy field, as a function of the frequency provides useful information on the soft magnetic character of the ribbons.

Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 magnets produced by injection casting

Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 hard magnets in rods were produced by injection casting method. Magnetic properties, phase evolution and microstructure for Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 magnets have been investigated and presented in as-cast and annealed states. The magnets possess soft magnetic characteristics in as-cast state, and hard magnetic characteristics after annealing. The Nb refines the grain sizes of α-Fe, Fe3B and Nd2Fe14B magnetic phases, while Y and Zr improve the glass forming ability. Good magnetic properties in Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 magnets arise from the microstructure composed of magnetically exchange coupled nanocrystalline α-Fe, Fe3B and Nd2Fe14B phases. Optimal annealed magnets of 2mm diameter and 30mm length demonstrate the hard magnetic properties, i.e. intrinsic coercivity jHc of 496kA/m, remanence Br of 0.76T and maximum energy product (BH)max of 72.0kJ/m3.

Effect of Dopants on the Microwave Magnetic Characteristics of FeCoBM-Al<sub>2</sub>O<sub>3</sub> Soft Magnetic Thin Films

A series of FeCoBM (M=Nb, Zr, Hf, Mo ,Ta, Ti)–Al2O3 films were prepared on glass and polymer substrates by means of RF magnetron co-sputtering. Effect of dopants on the soft magnetic properties and microwave magnetic characteristics of FeCoBM-Al2O3 Thin Films were studied. To further tailor the magnetic characteristics of the films, the (Fe40Co40B20)94.5Hf2.5–(Al2O3)3 film was annealed at 200 to 400°C for 60 min. As a consequence, the (Fe40Co40B20)94.5Hf2.5–(Al2O3)3 film annealed at 350°C exhibit excellent properties with high saturation magnetization of 1197 kA/m, high resonant frequency of 1.76 GHz, and the real part of permeability is about 600, which is maintained up to 1.5GHz. These results show that the presented films possesses potential in designing micro-magnetic devices for Monolithic Microwave Integrated Circuit (MMIC) and surface mount technology (SMT)industry.

Exchange bias of mu-metal thin films

The exchange bias of the soft ferromagnet mu-metal, Ni77Fe14Cu5Mo4, with the metallic antiferromagnet Fe50Mn50 has been studied as a function of ferromagnet thickness and buffer layer material. Mu-metal exhibits classic exchange bias behavior: the exchange bias (HEB) and coercive fields scale inversely with the ferromagnet's thickness, with HEB varying as the cosine of the in-plane applied field angle. Ta buffers, rather than Cu, allow the mu-metal to retain more of its soft magnetic character while exhibiting exchange bias. The ability to preserve soft ferromagnetic behavior in an exchange biased heterostructure may be useful for low field sensing and other device applications.

Microwave absorption performance of magnetic Fe–Ni–P nanoparticles electrolessly plated on hollow glass microspheres

Abstract Magnetic Fe–Ni–P nanoparticles have been successfully fabricated on hollow glass microspheres via electroless plating for the application of lightweight microwave absorbers. The resultant materials were characterized by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. The results show that compact and uniform Fe–Ni–P nanoparticles with the average diameter of about 150 nm have been successfully plated on the hollow glass microspheres. The plated microspheres exhibit excellent soft magnetic characteristics with high saturation magnetization and low coercivity, and the soft magnetic characteristic behaves better with the increasing of iron content in the coatings. Microwave absorption performance shows the maximum reflection loss of the composite powder reaches −49.2 dB at the frequency of 7.7 GHz with the thickness of 5 mm, and the bandwidth with the reflection loss less than −20 dB exceeds 2.2 GHz.

In situgrowth of FeNi alloy nanoflowers on reduced graphene oxide nanosheets and their magnetic properties

FeNi alloy nanoflowers were evenly grown on reduced graphene oxide (RGO) nanosheets by the reduction of Fe2+ and Ni2+ with hydrazine in an ethylene glycol (EG) dispersion of graphene oxide (GO), and the as-synthesized products were characterized by powder X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). It was revealed that the morphology, size and composition of the FeNi alloy nanoparticles on the RGO nanosheets can be well controlled by adjusting synthesis parameters such as the concentration and the molar ratio of the metal ions. Through directed-flow assembly of the obtained composite materials, RGO-based magnetic papers were obtained. The RGO-FeNi alloy composites had soft magnetic characteristics and showed interesting morphology and composition dependent magnetic properties.

Soft magnetic and microwave characteristics of amorphous FeCoBNi–Al 2O 3 films deposited by RF magnetron co-sputtering

A series of FeCoBNi–Al 2O 3 films were fabricated on glass and polymer substrates by means of RF magnetron co-sputtering. Firstly, the FeCoB films with Al 2O 3 addition were investigated. To further improve the microwave characteristics of the films, the effects of the Ni content on the soft magnetic properties and microwave characteristics of (Fe 40Co 40B 20) 97− x Ni x –(Al 2O 3) 3 films were studied. As a consequence (Fe 40Co 40B 20) 97–(Al 2O 3) 3 films doped with 28.64 at.% of Ni exhibit excellent properties with high saturation magnetization (4 πM s ) of 1.67 T, high resonant frequency ( f r ) of 2.58 GHz, high electrical resistivity ( ρ) of 235.85 μΩ cm and the real part of permeability is about 300, which is maintained up to 2 GHz. These results show that the presented films possesses potential in designing micro-magnetic devices design for Monolithic Microwave Integrated Circuit (MMIC).

Influence of Sputtering Gas Pressure on High-Frequency Soft Magnetic Properties of FeCoN Thin Film

In this paper, the influences of sputtering gas pressure on the high-frequency soft magnetic properties of FeCoN thin films are investigated. Both the static soft magnetic properties and microwave characteristics of FeCoN thin films are found to be highly dependent on the pressure. The high-frequency magnetic properties are characterized with permeability spectra and discussed based on the Landau-Lifshitz-Gilbert equation. The damping factor changes with sputtering gas pressure, and the resonance frequency shows an extraordinary large tunability with sputtering gas pressure. The effects are suggested to be related to the film stress which is affected by the sputtering pressure. This work provides a convenient method to tune the high-frequency magnetic properties of FeCoN film.

Effect of Dopants on the Soft Magnetic Properties and High Frequency Characteristics of FeCoBM (M = Ti, Nb, Hf, and Ta) Thin Films

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM thin films (M = Ti, Nb, Hf, and Ta) have been studied. For (Fe0.55Co0.45)(100-x)B(x) (x = 5-15) thin films, with the increase of B content, the resistivity was increased because B could decrease the crystallinity of the films. The (Fe0.55Co0.45)90B10 thin film showed the optimum properties, where 4piM(s) = 16.1 kG, H(ce) = 64.2 Oe, H(ch) = 13.5 Oe, H(k) = 310 Oe and p = 338 microomega-cm. To reduce the coercivity of the film, the elements M, including Ti, Nb, Hf, and Ta, were selected to substitute for B in the FeCoB films. It was found that (Fe0.55Co0.45)90B6Ti2Nb2 thin film after annealing at a temperature of 200 degrees C for 30 min showed the optimal properties, where 4piM(s) = 15.8 kG, H(ce) = 4.8 Oe, H(ch) = 3.6 Oe, H(k) = 224 Oe and p = 290 microomega-cm. The theoretically calculated ferromagnetic resonance frequency of the developed films can be higher than 5 GHz.

Microwave behavior in CoFe‐based single‐ and two‐phase magnetic microwires

AbstractThe ferromagnetic resonance (FMR), spectra in the frequency range up to 12 GHz has been investigated as a function of applied DC magnetic field (up to 80 kA/m) for single‐phase CoFe‐based Pyrex‐coated microwire as well as for biphase microwires after depositing an outer shell, with hard (CoNi) and soft (FeNi) magnetic character, respectively. In addition, a parallel study on the low‐frequency magnetic hysteresis loop of all these samples has been performed. In particular, we have focused on the influence of the thickness of the insulating Pyrex layer and magnetic character of the outer magnetic phase. For single‐phase microwires, the increase of the Pyrex thickness results in a continuous strengthening of the circular magnetoelastic anisotropy of the CoFe‐based core as deduced from FMR and confirmed by low‐frequency measurements. For biphase microwires three absorption peaks are observed: two of them can be ascribed to each magnetic phase since FMR frequencies obey the Kittel condition for a thin film. A third absorption peak is observed at lower frequencies that does not follow such an equation and can be ascribed to a pure geometrical effect of these biphase microwires.

The Migration Behavior of Atomic Clusters in Early Nanocrystalline Process of Soft Magnetic Finemet Alloy

The Finemet alloys are commonly used as cores in transformers and generators, stress and field sensors in technological application for their excellent soft magnetic characteristics. To clarify the nanocrystallization mechanism of Finemet especially about the atomic migration in early stage is very essential for developing their distinctive characteristics. In this study, we investigate the migration behavior of atoms in order to clarify the mechanism of the early-stage nanocrystallization in amorphous Finemet alloys. The Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous ribbons were prepared by single-roller melt-spinning process in argon atmosphere, and then annealed at 350 degrees C-400 degrees C for 10 minutes in vacuum. The atom force microscope (AFM) and the coincidence Doppler broadening spectra (CDB) were used to characterize the migration behavior of different atoms in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloy during the early-stage nanocrystallization. The X-ray diffraction (XRD) patterns show that all annealed samples are in the amorphous state. But the AFM observation shows clearly that there are many small atomic clusters (nuclei) which distribute in the amorphous matrix of the annealed samples. With increasing annealing temperature, there is a significant increase in the amount of atomic clusters and a dramatic drop in the average size of clusters with very limited Cu contention in the samples, which reflect the structural evolution into more homogeneity. The CDB spectrum indicates that the peaks of positron annihilation spectrum are gradually reduced, which means the number of grain boundary and the defects in samples are gradually increased. It can be concluded that more defects are introduced by the formation of atomic clusters through atomic migration during the early-stage nanocrystallization in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloys.