X. L. Yang

High-temperature giant magnetoimpedance in Fe-based nanocrystalline alloy

Giant magnetoimpedance (GMI) was investigated from room temperature up to 823 K in an Fe-based nanocrystalline Fe73.0Cu1.0Nb2.5V1.0Si13.5B9.0 ribbon. With an increment of the measuring temperature (T), GMI shows notable enhancement followed by a declining dependence, yielding a maximum value around 603 K where the relative GMI is nearly four times that at room temperature. The field at the peak of the GMI vs Hdc curve decreases monotonically with T, but around T=603 K there superimposes a trough-shaped variation. The thermal evolution of the soft magnetic property and magnetic anisotropy is suggested to be responsible for the high-temperature GMI features. Discussion on the intergrain exchange magnetic coupling through the amorphous boundaries in the two-phase Fe-based nanocrystalline alloy is also given.

Magneto-impedance effect in field- and stress-annealed Fe-based nanocrystalline alloys

Abstract The magneto-impedance (MI) effect in Fe-based nanocrystalline Fe 73 Cu 1 Nb 1.5 Mo 2 Si 13.5 B 9 alloys has been studied. The results showed that the field dependence of the MI ratio is strongly influenced by the transverse magnetic anisotropy in samples, which results from annealing in a transversal magnetic field or a longitudinal tensile stress. A large MI ratio of 100% and a slope of 660%/Oe were reached in samples exhibiting transverse anisotropy.

Longitudinally driven giant magnetoimpedance effect in stress-annealed Fe-based nanocrystalline ribbons

A high-frequency longitudinally driven giant magnetoimpedance (GMI) effect has been measured in stress-annealed Fe73Cu1Nb1.5V2Si13.5B9 nanocrystalline ribbons. Based on how the impedance phase varies with the external magnetic field, it becomes clear that the imaginary part of the complex permeability, μ″, which is related to magnetic losses, plays an important role in the high-frequency longitudinally driven GMI effect. The transverse anisotropy field Hk can be readily determined by a sharp minimum in the curve of the impedance phase as a function of the external magnetic field. This provides a new method for measuring the magnetic anisotropy field in such systems.

The GMI effect in nanocrystalline FeCuNbSiB multilayered films with a SiO2 outer layer

The giant magneto-impedance (GMI) effect in nanocrystalline FeCuNbSiB multilayered films was investigated. The multilayered films were deposited by magnetron sputter equipment with an additional SiO2 outer layer. The GMI ratio of multilayered films varied with the annealing temperature due to the changing orientation of the magnetic moments. The maximum GMI frequency of the nanocrystalline state was lower than that of the amorphous state, decreasing from 12.3 to 5.45 MHz. Ageing experiments were carried out for films with and without the insulator layer. It was seen that the GMI ratio of the multilayer film with a covered SiO2 layer was preserved well even after ageing.

Mössbauer studies of iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene

In-situ Mössbauer studies for dehydrogenation of ethylbenzene to styrene has been carried out. The results show that the formation of iron oxide is essentially Fe3O4 and there is no KFeO2 under the reaction condition. As a promoter, the existence of potassium is in favour of the electron exchange between Fe2+ and Fe3+ ions.

Resonance Enhancement of the Giant Magnetoimpedance Effect in Glass-Coated Microwires With Outer Conductive Layer

We investigated resonance enhancement of the giant magnetoimpedance effect in Fe-based glass-coated microwires with an outer copper layer. We found that a capacitance forms between the ferromagnetic core and the outer conductive layer, where the glass insulator works as a dielectric layer. The composite wire formed an LC resonance circuit by itself, resulting in an increase of magnetoimpedance ratio from 250% to 330%. Here, we explain the results in terms of the LC resonance enhancement principle.

A study of the action of magnesium on iron oxide catalysts for dehydrogenation of ethylbenzene to styrene

Mössbauer study of the action of magnesium on iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene has been carried out systematically. The presence of opportune amount of Mg enhances the stability and dispersivity of catalysts. Therefore Mg is one kind of useful structure promoter.

The effect of cerium on iron oxide catalysts for dehydrogenation of ethylbenzene

Abstract In situ Mossbauer study of ethylbenzene dehydrogenation on potassium-promoted iron oxide containing different contents of cerium oxide has been investigated. The results show that the addition of cerium to the FeK systems decreased the hyperfine magnetic fields for Fe3+ ions, due to the near neighbor and next near neighbor of Fe3+ ions to be partially occupied by cerium ions. In addition, the presence of cerium enhanced the stability of the FeK phase and reducibility of Fe oxide to Fe3O4 at the reaction condition.

The surfactant influence on the surface magnetic properties of Fe3O4 microcrystals

Mössbauer measurements, electron microscopy and infrared spectroscopy, have been used for investigating the Fe3O4 microcrystals coated with different surfactants. The experimental results show that the surface condition of the system changes and the anisotropy energy constantK of Fe3O4 microcrystals increases effectively when the surfactants being added. The spin pinning effect on a sample surface was observed and the pinning depth and the pinning direction were estimated. Besides, it has been shown that the anisotropy energy constantK of the coated Fe3O4 has an abrupt change nearbyTv.

Structure and magnetic properties of iron/cobalt-based glass-covered microwires

The changes in the structure and magnetic properties of FeCoSiBNi microwires have been investigated by means of differential scanning calorimetry (DSC), x-ray diffraction (XRD), 57Co Mossbauer spectroscopy and magnetization measurements. The crystallization temperature Tx value has been determined by DSC thermal analysis. XRD showed metastable phases (α-Fe/Co) that were formed in the nanocrystallization process. These metastable phases, embedded in the amorphous matrix, have a significant effect on magnetic ordering. Hysteresis loops and giant magneto-impedance effects measurement are used to determine the magnetic anisotropies as well as the magnetization processes.