Hongming Jin

Raman study on the effects of sintering temperature on the Jc(H) performance of MgB2 superconductor

The influence of sintering temperature on the critical transition temperature Tc and critical current density Jc for the MgB2 superconductor was investigated systematically with the observation of Raman scattering measurement and flux pinning force Fp analysis. The enhanced E2g mode in Raman spectra with increasing in situ sintering temperature shows gradual strengthening of the electron-phonon coupling in MgB2, which means that the crystals become more harmonic after higher temperature sintering. However, the crystal harmonicity is degraded for samples sintered at even higher temperature due to Mg deficiency. A possible explanation for the Jc(H) performance, which is in accordance with the Raman spectroscopy observation and Fp analysis, is the cooperation between the electron-phonon coupling in the E2g mode and the flux pinning centers, mainly originating from the lattice distortion due to the different sintering temperatures.

Synthesis of nano-crystalline Co3O4 particles by hydrothermal method under pulsed magnetic field

Nanocrystalline CO3O4 particles were successfully synthesized by hydrothermal method under pulsed magnetic field. The effect of magnetic field and aging time on the morphology and microstructure were examined. Different morphologies were observed from SEM images for the samples fabricated with or without pulsed magnetic field. The pulsed magnetic field made CO3O4 sphere compact and more smooth surface. The hollow sphere morphology and refined grain of CO3O4 were formed after aging process.

Effect of the Binder and Some Additives on Properties of the Anisotropic Injection Bonded Nd-Fe-B Magnets

Abstract This study is on the anisotropic Nd-Fe-B bonded magnets fabricated from HDDR powders by injection molding process under orientation magnetic field. The effects of polymer binder, chemicals such as coupling agent for surface modification of the powders, antioxidant and lubricant on the density, magnetic and mechanical properties of anisotropic Nd-Fe-B magnets were investigated. The corrosion resistance of the powder and magnetic properties of the magnets would be improved through the surface modification of the powders. Six kinds of binder and the amount of antioxidant and lubricant were studied. The magnetic properties of the anisotropic bonded Nd-Fe-B magnets fabricated under the following conditions of mixing temperature 205-215 °C, injection temperature 265 °C, injection pressure 5-6 MPa, press holding time 5 s, and molding temperature 80 °C, were as following: B r of 0.72 T , i H c of 983 kA/m, (BH) max of 75 kJ/m 3 .

TC ENHANCEMENT FOR NANO-SiC DOPED MgB2 SUPERCONDUCTORS SINTERED IN 5T PULSED MAGNETIC FIELD

The superconductivity of nano-SiC doped MgB2 sintered in pulsed magnetic field (PMF) was investigated with Raman scattering measurements and Raman spectral fit analysis. The critical transition temperature, Tc, for the sample sintered in 5T PMF is improved compared with that of the sample sintered without PMF. The high Tc is attributed to the strengthening of the electron-phonon coupling (EPC) in MgB2, as reflected by the broadened E2g mode in the Raman spectra. The EPC constants are estimated as 0.876 and 0.874, with the electron-E2g coupling contribution 2.30 and 2.25, respectively. Magnetic field processing technology has been proved to be a powerful tool to improve the superconducting properties of SiC-doped MgB2 superconductor.

Effects of Temperature on the Microstructure and Magnetic Property of Cr-Doped ZnO DMS Prepared by Hydrothermal Route Assisted by Pulsed Magnetic Fields

In the present work, Cr-doped ZnO diluted magnetic semiconductor was synthesized by hydrothermal method under pulsed magnetic fields. The samples were characterized by XRD, SEM, VSM, Raman, and XPS techniques. Results demonstrated that Zn ions in the ZnO crystal lattice were partially displaced by Chromium (III) ions. All samples show room temperature ferromagnetism which was enhanced by pulsed magnetic fields. The mechanism of ferromagnetism of Cr-doped ZnO particles was discussed.

Hydrothermal synthesis of ZnO nanostructures under high pulsed magnetic field

Crystalline zinc oxide (ZnO) particles with different morphologies have been synthesized by the hydrothermal method under the magnetic field. It is found that the magnetic field influences the nucleation and growth of ZnO crystals. ZnO crystals obtained under high pulsed magnetic field were more uniform and well integrated.

Effect of Pulsed Magnetic Field Processing on MgB2 Superconductors

Pulsed magnetic field was first employed in the study on MgB2 superconductors. Superconductivity properties and microstructures of Zn and SiC doped MgB2 were discussed in this paper. The superconductors showed different superconductivities after magnetic sintering. Critical current density and flux pinning force were relevant to the dopants properties in MgB2. Grains in the pulsed magnetic processed MgB2 matrix were smaller than those in the normal processed one. The refinement microstructures have caused the critical current density (Jc) anisotropy in both the Zn and SiC doped MgB2.

HYDROTHERMAL SYNTHESIS OF NANOCRYSTAL MNO2 UNDER PULSED MAGNETIC FIELD

Nanocrystal MnO2 was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO2 was studied by XRD and SEM analysis. It was found that the morphology of MnO2 has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

Transition metal-doped ZnO diluted magnetic semiconductors tuned by high pulsed magnetic field

Transition metal doped ZnO diluted magnetic semiconductors were synthesized by hydrothermal method under high magnetic field. Transition metal ions were incorporated into hexagonal wurtzite structural ZnO without secondary phases observed. High magnetic field can slightly improve real doped concentration and tune the magnetic property of TM-doped ZnO by controlling the type of dominant point defect.

Preparation of MnO 2 nanoflakes on Ti substrate by hydrothermal method

The preparation of birnessite manganese dioxides (MnO2) nanoflakes films on Ti substrate by hydrothermal method were studied in this paper. The structure and morphology were characterized by XRD and SEM. In conclusion, the material may have the great potential application as supercapacitor material.