Chao-Ming Fu

Magnetic and electrical properties of Mn–Zn ferrites synthesized by combustion method without subsequent heat treatments

Nanocrystalline ferrites MnxZn1−xFe2O4 (x = 0.0–1.0) were prepared by the combustion method without sequential heat treatment. As-synthesized MnxZn1−xFe2O4 ferrites, characterized by x-ray diffraction (XRD), have demonstrated a highly pure phase of spinel structure. From the analysis of XRD data with Scherrer’s formula, the average crystallite size is about 27–37 nm and the lattice parameters range from 8.457 to 8.515 A. The saturated magnetization of the Mn–Zn ferrite samples, measured by vibrating sample magnetometer, is varied with the content of manganese. The high frequency electromagnetic properties were investigated by impedance spectra methods and the conduction mechanism was also discussed. The results imply that this combustion method without further thermal treatment is relatively efficient and economical as compared to conventional methods for industrial synthesis of ferrites in high frequency electromagnetic devices applications.

High-frequency transport properties of spin-spray plated Ni–Zn ferrite thin films

The frequency and temperature variation of magnetoimpedance in Ni–Zn ferrite thin films fabricated by spray plating method were studied. It is observed that the frequency induces a metal–insulator crossover behavior in impedance spectra. The frequency behavior of the electrical properties of the film can be modeled by an equivalent circuit composed of resistance and capacitance. The relaxation time and activation energy of the conductivity were calculated. The result suggests that the high-frequency conductivity of the spin-spray plating of a Ni–Zn ferrite film is predominantly associated with the dielectric, rather than by magnetization, dynamics. Mechanisms underlying high-frequency transport are discussed.

A comparison of ferroelectric liquid crystals containing diastereomeric propionic acids derived from natural ethyl lactate

Two diastereomeric carboxylic acids, 2(S)-[2(R)-methylhexyloxy]propionic acid and 2(S)[2(S)-methylhexyloxy]propionic acid, were prepared from ethyl (S)-lactate and (R)-1-iodo2-methylhexane or (S)-1-iodo-2-methylhexane in the presence of Ag2O. From these acids two liquid crystals, 2 and 3, whose configurations are (S, R) and (S, S) were synthesized and their liquid crystal properties investigated. Although both LCs have the same phase sequence Cr-SmC*-N*-I as well as a wide SmC* phase range, the influence of the relative stereochemistry on their physical properties is clear. The liquid crystal with (S, S)-configuration possesses better properties: lower SmC* phase transition temperature, wider SmC* phase range and higher Ps value. The Ps value difference between the ferroelectric LCs 2 and 3 (97 and 131nCcm-2, respectively, at Tc - T = 10°C) is unexpectedly large. The consideration, alone, of a zigzag conformation at the chiral molecular part of 2 and 3 is insufficient to explain such a difference.

Effect of the naphthalene moiety on the mesogenic properties of ferroelectric liquid crystals containing diastereomeric propionic acids

Two ferroelectric liquid crystals containing the naphthalene moiety were synthesized from 2(S)-[2(R)-methylhexyloxy]propionic acid and its (S, S)-diastereomer. Their mesogenic properties are compared with those of the analogous mesogens containing the biphenyl ring.

Giant magneto-impedance effects in sintered La1−xCaxMnO3 oxides

Abstract We report on the study of high-frequency magneto-transport properties in the sintered La 1− x Ca x MnO 3 oxides. Experimental results have demonstrated a giant magneto-impedance (GMI) effect, much larger than the DC magneto-resistive effect, in these manganese oxides. The temperature and frequency dependence of the magneto-impedance is dependent on the ratio of Mn +3 /Mn +4 and the magnetic phase state in these compounds. Our result implies a possible sensitive probe of complex phase states at high frequency and the further technical GMI applications.

Effect of Magnetostriction on the Core Loss, Noise, and Vibration of Fluxgate Sensor Composed of Amorphous Materials

This paper presents a new multistructure fluxgate magnetic sensor composed of Metglas® Fe-based amorphous HB1 material. The core thickness of the fabricated structure is 0.0254 mm × 30 pieces, and its width is 5 mm. The magnetic loss of the fluxgate core is simulated through finite element analysis. The fluxgate sensor is experimentally analyzed over a frequency range 0.5-3 kHz. The sensor performance exploits the advantages of the multistructure core-shaped magnetic material as well as the second-harmonic operation mechanism. Excellent flux responses are detected for the triangular core sensor, which has different operating frequencies for magnetostriction variation, harmonic response, total harmonic distortion, noise level, sensor vibration, and sensitivity. The influence of magnetostriction, magnetic loss, and permeability in multiangled cores for different frequencies is analyzed. Our multistructure fluxgate sensor is suitable for various applications including power transformer and inverter for interior magnetic core fault detection, owing to its thin-film configuration, high sensitivity, high resolution, and low magnetic loss.

High frequency impedance spectra on the chromium dioxide thin film

We report on the study of high frequency magnetotransport properties of the chromium dioxide (CrO2) thin films, grown on Si substrate using chemical vapor deposition. The film exhibits a ferromagnetic transition with a Curie temperature near 390 K. The temperature dependent spontaneous magnetization follows Bloch’s law. The impedance spectra, being analyzed based on the fundamental electrodynamics, are demonstrated to be in a low-loss dielectric limit along with the occurrence of dielectric relaxation and magnetization response. The specific features of impedance spectra, distinct from the usual metallic ferromagnet, are attributed to the half metallic nature of CrO2. The results explore the possibility for high frequency device applications.

In vivo bio-distribution of intravenously injected Tc-99 m labeled ferrite nanoparticles bounded with biocompatible medicals

Superparamagnetic nanoparticles have been widely utilized for in vivo or in vitro biomedical applications. Knowledge on the distribution of injected particles in organs is necessary to gain access to diagnosis or therapeutics. Thus, an in vivo study on the bio-distribution of the directly Tc-99m-labeled ferrite nanoparticles which were intravenously injected into tail vein of Wistar rats is performed. The dynamic bio-distribution was monitored by gamma camera. The scintigrams show that the injected dose are taken up by liver and lung. From dynamic scintigraphic image, it is observed that the uptake of particles by the organ is very fast and completed within first few minutes after intravenous injection. To investigate to what extent the Tc-99m labeled ferrite beads can be further conjugated with therapeutic drug, poly(ethylene glycol) (PEG) and two types of herb medicines, i.e. the Gentiana comnination and Trionyx sinensis with a function for chronic hepatitis, were sequentially conjugated with the ferrite adio-beads. It is demonstrated that the relative radioactivity of liver compared to that by lung and heart is lowered by the PEG modification. We also have performed in vivo study by applying the commercially available Nd-Fe-B magnet onto the site before intravenous injection into rat. The result implies that the directly Tc-99m labeled ferrite nanoparticles, conjugated with biocompatible medicals, may implicate for diagnostic and therapeutic applications.

Magnetically directed targeting aggregation of radiolabelled ferrite nanoparticles

Ferrite magnetic nanoparticles (Fe3O4 or iron (II, III) oxide; 15-25nm of diameter) were developed. These magnetic nanoparticles are a potential vehicle for magnetically induced target aggregation in living animals. In this preliminary study, the radiochemical purity for the radiolabeled magnetic nanoparticles was examined, and the possibility of the magnetically induced targeting of the radio-nanoparticles was evaluated. Our results showed that radiolabeled ferrite nanoparticles can be used as magnetic targeting agents with high labeling efficiency and stability. These particles can be distributed within living animals via intravenous injection, and the biodistribution of the particles can be potentially controlled by external magnetism. These evaluations will be the groundwork for the future development of delivery techniques for radiopharmaceuticals through external magnetic control.

Optical Transmittance and Dynamic Properties of Ferrofluids (Fe

The dynamic property of ferrofluids under a dc-biased magnetic field was understood by the measurement of optical transmittance. The results show that immediately after the application of a magnetic field, the transmitted optical intensity decreases to a minimum and, then, increases until it becomes stable. From the microscopic images, they indicate that this effect is due to longitudinal aggregation of the magnetic nanoparticles, forming chains. When the chain-like structure was formed by the applied magnetic field, the optical transmittance was decreasing. As the chains became longer and the distance between chains is larger, the transmittance was increasing. Moreover, our experiment result shows that this dynamic process is influenced by a different applied magnetic field, sample concentration, and carrier fluid.