•Cryogenic and thermal cycle treatment on the GMI in Co-based ribbon was studied.•Oxidation state of the ribbons after treatment is evaluated by XPS.•Changes in surface roughness and magnetic domain structures of ribbons were studied.•The GMI ratio was increased from 89% to 104% and 130% at 1 MHz the treatment.•The AGMI occurred and the GMI sensitivity was improved from 10%/Oe to 33%/Oe.The influence of cycle rapid cooling treatment on the giant magnetoimpedance (GMI) properties in Co-based amorphous alloys was investigated. Hysteresis loops show that the saturation magnetization of ribbons has been improved by cycle treatment. It can be found that the GMI ratio was increased from 89% to 130% at 1 MHz by the thermal cycle (TC) treatment. Moreover, GMI ratio of TC treatment sample increased up to 321% at 5 MHz. It is considered that internal thermoelastic stress leads to surface roughness, magnetic domain structures and saturation magnetization changes of the ribbons during different cycle processes. It was also found that the asymmetric GMI (AGMI) phenomenon occurred in the Co-based alloys with TC treatment after annealing, which can be regarded as a new method to get GMI-valve to improve GMI sensitivity.

•We have successfully prepared FeCoC soft magnetic films by electrochemical deposition method.•The resonance frequency can be controlled by changing pH value.•A widely absorption peak will be obtained when the pH value is appropriate.FeCoC films were successfully prepared by electrochemical deposition method in different citric acid concentrations and pH values. The morphology, structure and magnetic properties were investigated. FeCoC films deposited at different citric acid concentrations have good soft magnetic performance. As the pH value increases from 2.49 to 6.02, the atomic ratio of Fe:Co range from 0.72 to 0.95. The coercivities of the films deposited at different pH values first increase and then decrease with increasing pH. The resonance frequency of the films can be tuned by controlling the pH value, and in an appropriate pH value a wide absorption peak can be obtained.

L10-structured platinum–iron (FePt) nanofibers were successfully synthesized by electrospinning technique, followed by calcination and reduction processes. In the preparation procedure, ferrous chloride tetrahydrate [Fe(Cl)2⋅4H2O] and iron nitrate nonahydrate [Fe(NO3)3⋅9H2O] were, respectively, used as iron sources contained in precursor solution for electrospinning. Subsequently, the FePt nanofibers were obtained from the calcination in air and the followed reduction in hydrogen (H2) of the as-spun FePt/PVP composite nanofibers. The FePt nanofibers were characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, and superconducting quantum interference device magnetometry. It was found that the different iron salt used in the spinning solutions could highly affect the FePt nanofiber morphology, crystallite size, and the magnetic properties. The FePt nanofibers, resulted from the spinning solution containing iron dichloride tetrahydrate, were of better crystallinity and well-defined fibrous morphology with an average diameter of about 110 nm. Additionally, the considerably large coercivity of 10.27 kOe was recorded from the above FePt nanofibers.

•Graphene-based magnetoimpedance material has been successfully prepared.•Soft magnetic FeNi alloy covered the both surfaces of graphene paper by electrochemical deposition and magnetron sputtering.•Stratified FeNi/graphene/FeNi composite exhibited an enhanced magnetoimpedance effect.Enhanced magnetoimpedance effect has been observed in graphene-based composite materials. Graphene papers were synthesized in large quantities using a modified chemical approach. Two methods have successfully prepared the FeNi/graphene/FeNi composite: electrochemical deposition and magnetron sputtering. For the electro-deposited sample, graphene paper turns crumpled and the deposited FeNi looks like flower-petals. While for sputtered FeNi films on graphene paper the layered structure was observed distinctly. Both samples show magnetoimpedance effect at low frequencies. Especially, the stratified FeNi/graphene/FeNi composite exhibited an enhanced magnetoimpedance effect, which is about 10 times as large as single FeNi film or multilayer film structure at low frequency.

FeCoZr soft magnetic films with amorphous structure were electrodeposited onto ITO conductive glass substrates from the electrolytes with different composition and deposition potential. The factors which affect the deposit composition were discussed. The in-plane uniaxial magnetic anisotropy of film intensively depended on the concentration of boric acid. The coercivity of thin films decreased significantly with the composition gradient of doping Zr element. The ferromagnetic resonance frequency was as high as 3.4 GHz. Therefore, these films have a wide range of applications in the high-frequency field.Highlights► FeCoZr alloy films are prepared on ITO by electrochemical deposition. ► The structure of films is influenced by electrodeposition parameter. ► The in-plane magnetic anisotropy intensively depends on additives in electrolyte. ► The doping of Zr element effectively decreases the coercivity of films. ► The resonance frequency can reach 3.4 GHz.

Cu1−xZnxFe2O4 (0 ≤ x ≤ 1) nanofibers with continuous and fibrous morphology have been prepared by electrospinning combined with sol-gel method. The effect of Zn substitution on structure, morphology and magnetic properties were studied extensively. Scanning electron microscope and transmission electron microscope results reveal that Zn substitution strongly improves the poor morphology of the CuFe2O4 nanofibers. It was found that with increasing Zn content, the saturation magnetization initially increases and then decreases with a maximum value of 58.4 emu g−1 at x = 0.4, whereas the coercivity and square ratio decrease monotonously. Interestingly, the magnetic easy axis of the Cu0.6Zn0.4Fe2O4 nanofibers is not totally along the long axis of the nanofibers, which might due to the loosely connected nanoparticles and/or the dipolar interactions between these nanofibers.Highlights► Zn-doped CuFe2O4 nanofibers have been prepared by electrospinning. ► Zn content improves morphology of doped nanofibers and decreases the diameter. ► Saturation magnetization of nanofibers initially increases and then decreases. ► The coercivity and square ratio all decrease with increasing Zn2+ content. ► Cu0.6Zn0.4Fe2O4 nanofibers exhibit shape anisotropy.

ZnO nanoflowers were successfully prepared by a new non-catalytic method based on directly heating of Zn strip using a direct current power supply. The Zn strip was obtained by electrodeposition on silicon wafer with laser etching. The nanoflowers, with a size more than 15 μm, are assembled by nanowires with a length of 10 μm and a diameter of 100 nm, and the length/diameter ratio is about 100. The samples were characterized by means of scanning electron microscope, X-ray diffraction and Raman. X-ray diffraction results show that the formation of nanoflowers is controlled by the current density. Raman modes of nanoflower corresponds well with X-ray diffraction result. Photoluminescence property of ZnO nanoflowers shows strong green emission and violet emission.Highlights► ZnO nanoflowers were successfully prepared by a new non-catalytic method. ► Large-scale preparation of nanoflowers is fast. ► These nanoflowers from nanowires have an extraordinarily high length/diameter ratio. ► Photoluminescence property of ZnO nanoflowers shows strong green emission and violet emission.

Carbon-encapsulated Fe nanoparticles have been successfully synthesized by a two-step procedure method of hydrothermal and subsequent thermal reduction process. The introduction of hydrogen atmosphere helps to obtain pure α-Fe phase and the lower annealing temperature (at 550 °C). The morphological characterization indicates that the nanoparticle presents a quasi-spherical shaped, core–shell structure with diameter ranged from 10 to 20 nm and a carbon shell of about 4 nm. The results of X-ray diffraction and Raman spectrum demonstrate that carbon in the as-synthesized product is in amorphous phase. Magnetic measurements reveal the ferromagnetic behavior of the product.Highlights► Fe/C core–shell nanoparticles have been synthesized by a two-step procedure. ► The nanoparticles show a quasi-spherical shaped, core–shell structure with diameter ranged from 10 to 20 nm and a carbon shell of about 4 nm. ► The introduction of H2 helps to achieve lower annealing temperature of 550 °C to obtain Fe phase. ► Hydrogen atmosphere facilitates the formation of pure α-Fe phase while annealing.

Ba2Co2Fe12O22 (Co2Y) was synthesized by sol–gel method using glucose as chelating agent. X-Ray diffraction studies indicate that sintering temperature as low as 950 °C is sufficient to produce Co2Y ferrites. Co2Y ferrites calcined at 1,000 °C exhibit good magnetic prosperities in high frequency, with the resonance frequency up to 11 GHz and intrinsic permeability about 5 even at 6 GHz. The heat-treated temperature dependence of coercivity, initial permeability and resonance frequency is close related to the particle shape and size.

Size and shape controlled fabrication of magnetic Co microsphere, nanoribbon, nanochain and rose-like microarchitecture has been successfully realized via a simple hydrothermal route. X-ray diffraction analysis suggests that Co hierarchical nanostructures are identified as hexagonal phase. Magnetic hysteresis measurements demonstrate that the obtained different Co hierarchical structures show structure-dependent magnetic properties. Saturation magnetization (MS) found for Co spherical flowers and spherical powders are larger than Co nanoribbons, smaller than sphere-rebuilt micro particles or chain-like structures. Chain-like and nanorribon structures have abnormally large coercivity (HC). HC values of Co nanoribbons and one dimensional chains become as large as 256 Oe and 316 Oe.

Electrospinning is a novel technique used to fabricate nanometers to micrometers diameter polymeric and ceramic fibers. The morphology and structure of fibers which would be dominated by electrospinning process parameters and calcinations conditions are important when considering practical applications. This paper involves an investigation of how heating rate influence morphology and structure of CoFe2O4 nanofibers. The morphology of CoFe2O4 nanofibers changes from a continuous fibrous structure for low heating rate to a winding and packed crystallites nature for high heating rate, increasing heating rate also causes an increase in diameter. FTIR and XRD results demonstrate that PVP/CoFe2O4 composite nanofibers for all heating rate form CoFe2O4 cubic phase with very high crystallinity after calcinations.Highlights► Morphology of CoFe2O4 nanofibers has been studied with heating rate 1–6 °C/min. ► Continuous and smooth surface are observed when heating rate less than 4 °C/min. ► A dramatic change in morphology takes place with increasing heating rate. ► The crystal structure shows little change with different heating rate.

To tailor coercivity and magnetic anisotropy, we have fabricated Co nanowire arrays in the pores of anodic aluminum oxide templates by electrodeposition. Microstructure measurements performed by X-ray diffraction show that Co nanowire arrays are hexagonal close-packed (HCP) structures with different crystalline textures. A wide range in change of coercivity from 925 to 3310 Oe at 300 K, with a maximum of up to 4050 Oe at 5 K, can be found for nanowire arrays with a diameter of 20 nm. This may be the highest value and the widest range of coercivity reported for Co nanowires prepared by electrodeposition method. This finding could be attributed to the adjustment of the microstructure of the cobalt nanowire arrays prepared in different experimental conditions. We have also investigated the relationship between the crystalline textures and the magnetic properties of Co nanowire arrays using micromagnetic simulation combined with microstructure measurements. The preferred orientation of nanowire arrays, such as (1000) or (0002), is a key factor in determining coercivity. This wide tailoring of coercivity makes possible more promising applications of Co nanowire arrays with fixed diameter and length.

With a bottom-up assemble technology, heterogeneous magnetic nanobrushes, consisting of Co nanowire arrays and ferromagnetic Fe70Co30 nanofilm, have been fabricated using an anodic aluminum oxide template method combining with sputtering technology. Magnetic measurement suggests that the magnetic anisotropy of nanobrush depends on the thickness of Fe70Co30 layer, and its total anisotropy originates from the competition between the shape anisotropy of nanowire arrays and nanofilm. Micromagnetic simulation result indicates that the switching field of nanobrush is 1900 Oe, while that of nanowire array is 2700 Oe. These suggest that the nanobrush film can promote the magnetization reversal processes of nanowire arrays in nanobrush.

Nanocrystalline BaFe12O19 powders are successfully synthesized by using glucose as a fuel. The effects of the calcination temperature on the morphology, crystalline structure and magnetic properties of the barium ferrite particles are characterized by thermal gravimetric/differential thermal analyzer, field emission scanning electron microscope, X-ray diffractometer and vibrating sample magnetometer. Pure barium ferrite powders with a crystal particle size of 60 nm are obtained at temperature as low as 900 °C, showing a saturation magnetization (Ms) of 53 emu/g, a coercivity (Hc) of 5.3 kOe and a squareness of 0.573.

•Micromagnetic simulation for detecting magnetic nanobeads is performed by using a spin torque oscillation as a detector.•An 80-nm-diameter magnetic bead can be detected with a frequency shift of 1.2 GHz and a maximum linewidth of 28 MHz.•For multiple beads detection, the oscillation frequency is linear with the number of 40-nm-diameter beads, namely 0.16 GHz/bead on average.Micromagnetic simulation for detecting magnetic nanobeads is performed by using spin torque oscillation as the detector. The non-uniform stray field generated by magnetic beads can induce a detectable frequency shift of a spin torque oscillator. Simulations indicate that an 80-nm-diameter magnetic bead can be detected with a frequency shift of 1.2 GHz and a maximum linewidth of 28 MHz. Due to the non-uniform stray field, the frequency shift and linewidth vary with the bead position. For multiple beads detection, the oscillation frequency is linear with the number of 40-nm-diameter beads, namely 0.16 GHz/bead on average.

•A phenomenological model is proposed to analyze the angular dependence of the μ″max.•The maximum canting angle θ0 in the stripe domain structure can be estimated.•Micromagnetic simulation results are nearly in accordance with the experimental results.An investigation of the angular dependence of the dynamic permeability spectra has been performed. Three Permalloy films with different thickness were used as the study samples that possess the stripe domains. In order to better understand the magnetization distribution in stripe domains, a theoretical approach was proposed to analyze the variation of the resonance intensity of permeability spectra. By fitting the angular dependence of the μ″max using a theoretical function, a coefficient Λ that can be used to evaluate the average value of the periodic function of the anting angle θ in a periodic stripe is obtained. As the film thickness increases, the decrease of the ratio between domain wall width and stripe domain width is happen. This enables that the coefficient Λ decreases with the increase of film thickness. By deducing this coefficient Λ, one can estimate the maximum canting angle θ0 ∼ 8° for the Permalloy films in our experiments.