Papers by Keyword: Magnetic Property

Abstract: When applied to devices, BaM ferrite materials are required to have magnetic properties such as high saturation magnetization, or microwave properties such as low ferromagnetic resonance linewidth, which require BaM ferrite to be as dense as possible. The density of BaM ferrite can be significantly improved by introducing pre-holding in the sintering process. The density of BaM ferrite can reach 5.06 g/cm³, the sample grain size can reach 100 μm, and the magnetic properties are close to the single crystal state after 1 h of pre-holding. The maximum 4πM_s is 4606 Gs and ΔH is 487 Oe when pre-holding for 1 h, indicating its potential for application in microwave devices.

Abstract: This study aims to synthesize, purify, and modify magnetic carbon nanofibers (Mag-CNF) into hydrophilic carbon material. The synthesis method was carried out by chemical vapor deposition (CVD) using the catalyst from Incolloy at 800°C with argon, nitrogen, hydrogen, and acetylene gases. The purification of Mag-CNF was then conducted by dissolving Mag-CNF with toluene and ethanol, followed by vacuum annealing. The hydrophilization of Mag-CNF was further performed by adding amine groups via reacting Mag-CNF with ethylene diamine, NaNO₂, and H₂SO₄. The successfully prepared Mag-CNF has characteristics of tubular tube bundles consisting of carbon nanofibers with an average diameter of 100-120 nm. The X-ray diffraction (XRD) profile shows the characteristics of carbon, iron, iron oxide, and iron carbide. The Raman spectra show the existence of D, G, and G' bands corresponding to the characteristics of carbon nanomaterials. The magnetic property characterization using a vibration sample magnetometer (VSM) shows the synthesized product as ferrimagnetic materials. The modification results show the addition of hydrophilic groups to Mag-CNF, such as O–H and N–H groups, as analyzed in Fourier Transform Infrared (FTIR) spectra. The successful hydrophilization was also visually confirmed using a dispersion test in water, showing that Mag-CNF has better dispersion after surface modification.

Abstract: In this work, a diagnostic application was performed by utilizing magnetic nanoparticles for the bio-sensing. A novel Fe₃O₄ nanostructure was synthesized in this paper using a simple hydrothermal method, the Fe₃O₄ nanoparticles are successfully controlled to provide a more dynamic site for catalytic reaction. FTIR-analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) was used to examine the morphology of the synthesized nanoparticles. The findings showed that a unique Fe₃O₄ nanostructure was obtained nanoparticles confined in nanosphere. The relative catalytic kinetics of Fe₃O₄ nanostructure has followed Michaelis–Menten behaviours, according to an analysis of peroxidase-like activity. An effective approach for colorimetric sensing of glucose was formulated on the bases of efficient peroxidase-mimicking activity of Fe₃O₄ nanoparticles. The synthesized Fe₃O₄ nanoparticles are very hopeful for the application of bio-sensors.

Abstract: Multilayer films exhibit high saturation magnetization, high permeability, and high cutoff frequency f_r, applying to magnetic inductors that satisfy both high frequency, miniaturization, and integration. In this work, we fabricate Fe/Ni₈₁Fe₁₉/Fe (t/100/t nm) multilayer films on Si (100) using electron beam evaporation, and investigate the Fe thickness dependence of surface morphology, saturation magnetization, coercivity, and ferromagnetic resonance f_r. The results demonstrate that Fe/Ni₈₁Fe₁₉/Fe (4/100/4 nm) multilayer film possess relatively high saturation magnetization (12.1 kGs), low coercivity (3.1 Oe), and high ferromagnetic resonance f_r (1.93 GHz).

Abstract: Numerous studies have been conducted to develop next-generation recording technology in spintronics. Because ultrafine magneitc particles are vital components of the technology, the interplay between the microsturcture and magnetic properties has attracted attention extensively in recent years. We focused on the relationship between the microstructure and magnetic properties of Cu-Ni-X (X=Fe, Co, FeCo) alloys comprising nanogranular magnetic particles. In this work, we prepared Cu-20 at% Ni-5 at% (FeCo), Cu-20 at% Ni-5 at% Fe, Cu-20 at% Ni-5 at% Co and examined the changes of microstructure and magnetic properties associated with heat treatments and composition. To examaine microstructural evolution of the alloy specimens, we conducted transmission electron microscope observations (TEM) with the as-quenched specimens and those aged at at 773-1073 K. We also carried out magneto-thermo gravimetry (MTG) measurements, superconducting quantum interference device (SQUID) measurements, magnetoresistance (MR) measurements and first-principles calculations based on the Koster-Korringa-Rostker (KKR) method with the Coherent Potential Approximation (CPA), to investigate the magnetic properties. The present work confirmed that the microstructure significantly changed, depending on the composition and heat treatment conditions. The present work also revealed that the magnetic properties closely correlated with the microstructure of samples.

Abstract: Nano-scale granular magnetic material is a core component in next-generation recording devices. We investigated the influences of element species and composition of ferromagnetic atoms in copper-nickel base nanogranular magnetic materials. In this work, the authors focused on how microstructural evolution and magnetic properties are correlated in Cu-20at%Ni, Cu-15at%Ni-5at%Co and Cu-15at%Ni-5at%Fe alloys. We used Magneto-thermogravimetry (MTG), superconducting quantum interference device (SQUID) magnetometry and first-principles calculations based on the method of Koster-Korringa-Rostker (KKR) with the Coherent Potential Approximation (CPA) in order to investigate magnetic properties. Transmission electron microscope (TEM) observations revealed that ferromagnetic element atoms were precipitated with annealing at 973K, but microstructures were changed, depending on the combination and composition of the solute atoms. The magnetic property measurements and first-principles calculations have confirmed that magnetic precipitates are responsible for the magnetic properties of the Cu-Ni-Co and Cu-Ni-Fe alloys.

Abstract: Features of obtaining magnetic nanocomposites based on the lattice packing of SiO₂ nanoscale (opal matrices) with clusters of multiferroic materials (Li-Zn, Bi, Fe, Dy, Gd and Yb titanates) in their interstitial cavities have been considered. For magnetic nanocomposites creation opal matrices with SiO₂ nanoscale of ~ 260 nm in diameter have been used. The composition of nanocomposites has been also studied using X-ray diffractometry and Raman spectroscopy. The results of the frequency dependences measurement for the dielectric constant of the nanostructures obtained have been presented. Hysteresis loops have been examined for the samples obtained in the temperature range from 2 to 400 K.

Abstract: Pure iron with C/Si > 1 and C/Si < 1 was smelted by a vacuum arc furnace, and the grain size was controlled through different heat treatments. The microstructure of pure iron was observed by using an optical microscope, and the grain size was subsequently measured and calculated. Finally, the coercive force, saturation magnetic induction, and permeability were measured using a vibrating sample magnetometer. The results indicate that the coercive force increases with decreases in the average grain diagonal size. An increase in the uniformity of the grain increases the saturation magnetic induction. The permeability depends on the average grain diagonal size and the uniformity of the grain as well as the chemical composition of pure iron.

Abstract: A series of Fe_75.5-xNi_xCu₁Nb₃Si_12.5B₈ (x=0.5-10 at. %) soft magnetic dual-phase alloys with low permeability were synthesized by adjusting Ni content. Effect of annealing on the soft-magnetic properties, crystallization behavior and microstructure were investigated. It is found that the temperature interval between the two crystallization temperature is significantly decreased from 169 to 127°C when the Ni content of the alloys increases from x=0.5 to x=10, which greatly reduces the optimum annealing temperature range. The alloys with higher Ni content are prone to exhibit lower permeability, and the alloys with the composition of Fe_65.5Ni10Cu₁Nb₃Si_12.5B₈ exhibit excellent soft-magnetic properties, including the low permeability of 3350, low coercivity of about 1.26 A/m and low remanence of 8 mT. The combination of low permeability and excellent soft-magnetic properties makes the FeNiCuNbSiB nanocrystalline alloys to be a kind of promising material for common mode chokes and current transformer with direct current tolerance.

Abstract: It is well-known that apatite has high affinity to many kinds of biomolecules. In this study, the authors aimed to develop the apatite microcapsules with both enzyme immobilization property by the bioaffinity of apatite and magnetism of core materials. The authors encapsulated maghemite particles, possesing ferrimagnetism, with apatite by attaching Apatite Nuclei on the surfaces of maghemite particles and subsequently immersing them in SBF. To evaluate performance of the microcapsules as enzyme immobilization carriers, the authors investigated enzyme immobilization property of the microcapsules fabricated by biomimetic method using Apatite Nuclei and SBF from the viewpoint of the difference of isoelectric point of the three-types of enzymes.