Fuxiang Cheng

Nanophased CoFe2O4 prepared by combustion method

The combustion method has been utilized to prepare nanophased powders of cobalt spinel ferrite using glycine as fuel. Structural and magnetic properties of the products were investigated with an X-ray diffractometer, a surface analyzer, and an alternating gradient magnetometer, respectively. Cobalt spinel ferrite prepared by the present method can easily form the well-crystallized nanoscale particles with a large specific surface area. The magnetization and coercivity show a strong dependence on the G/N (glycine to nitrates) ratio in the range from 0.2 to 1.0.

MICROSTRUCTURE, MAGNETIC, AND MAGNETO-OPTICAL PROPERTIES OF CHEMICAL SYNTHESIZED CO-RE (RE=HO, ER, TM, YB, LU) FERRITE NANOCRYSTALLINE FILMS

The sol-gel synthesis of Co–RE (RE=Ho, Er, Tm, Yb, Lu) ferrite nanocrystalline films was accomplished on monocrystalline silicon substrates, and the influence of RE ions on structure, magnetic, and magneto-optical (MO) properties of the resultant ferrites was examined. The results obtained reveal that, when x⩽0.2, the CoFe2−xRExO4 ferrite films have pure spinel phase with slightly enlarged cell constants and lattice distortion due to the large radii of RE ions. The RE ions tend to decrease the room-temperature magnetization as well as the Curie point of products, and may have a certain contribution to coercive force except for a nonmagnetic Lu3+ ion. For the present optical structure in which MO layers are substrated on silica, Co–RE ferrite films show the peak Kerr rotation at a shorter wavelength than the CoFe2O4 film, and Er or Tm doped samples exhibit an interesting enhancement of the MO effect.

Nanostructure magneto-optical thin films of rare earth (RE=Gd,Tb,Dy) doped cobalt spinel by sol–gel synthesis

Nanocrystalline CoFe1.9RE0.1O4 [rare earth (RE=Gd,Tb,Dy)] films have been prepared by the sol–gel route, and their polar magneto-optical (MO) Kerr rotation and ellipticity have been determined in the spectral range of 4000–8000 A. The films are composed of nanometer grains with the spinel structure. RE doped cobalt spinel ferrites are found to have dramatic changes in magnetic and MO properties, with increases in their coercive force and enhancement of the MO rotation in the Tb3+ doped sample.

Chemical synthesis and magnetic study of nanocrystalline thin films of cobalt spinel ferrites

The sol-gel method was introduced to prepare the nanocrystalline thin films of cobalt spinel ferrite, which presents a convenient approach to perform the doping of foreign ions. The dependence of morphology and grain sizes of thus-obtained thin films on the annealing temperature were observed. Nanocrystalline thin films of CoFe2O4 have relatively lower magnetization than bulk phase and negative interactions between magnetic grains, the latter of which may be of significance to reduce the media noise for polycrystalline materials.

A large low field colossal magnetoresistance in the La0.7Sr0.3MnO3 and CoFe2O4 combined system

La0.7Sr0.3MnO3 and CoFe2O4 samples have been prepared by a sol-gel process. A mixture of the two samples was annealed at 800 °C and the scanning electron micrograph shows large CoFe2O4 grains well surrounded by La0.7Sr0.3MnO3 grains. The powder x-ray diffraction patterns indicate no evidence of reaction between the La0.7Sr0.3MnO3 and CoFe2O4. The resistivity of the combined sample (with 20 wt% CoFe2O4) is about an order of magnitude larger than that of the same-grain-sized La0.7Sr0.3MnO3 sample, while a large low field magnetoresistance (MR) has been obtained in the combined samples. Under an applied field of 5 kOe, the MR of the combined sample is 10% even at 280 K and 5% at 290 K, whereas the same nanosized La0.7Sr0.3MnO3 sample is only 2% and 1%, respectively.

The sol-gel preparation and AFM study of spinel CoFe2O4 thin film

Abstract The thin films of CoFe2O4 spinel ferrite were prepared on the substrates of monocrystalline silicon(100) at low temperature by means of a developed citrate processing. According to the AFM observation and XRD studies, several key processing parameters were optimized. In the coating solution, the volume ratio of the mixed solvents water/ethanol, the concentration of citric acid and that of PEG were chosen as 1:8, 0.2 mol/l and 40–80 mg/ml, respectively. The films resulted from the annealing of thus-obtained film precursors at 630–679°C for 1 h possess high quality surface and well-crystallized spinel structure. The methods presented in this paper makes it very convenient to perform substitution of foreign ions.

Clean separation technologies of rare earth resources in China

Abstract After a review on the conventional separation process of rare earths (RE), hyperlink extraction technology was introduced and a potential process was proposed for clean separation of RE. A great amount of acid, base and water was consumed in the conventional RE separation process which included the procedures of raw material dissolving, extraction separation and precipitation. Therefore hyperlink extraction technology had been developed, by which the repeated consumption of acid and base could be avoided during the extraction process. And based on the theory and successful applications of the hyperlink extraction technology, we proposed the integral hyperlink process in which the intermediate acid resulted in individual procedures would be recycled and reused after being treated. The proposed process would make it feasible to consume no chemicals except for oxalic acid, and so could be a promising clean separation technology with a significant reduction on consumption and emission.

Low temperature synthesis and magnetism of La0.75Ca0.25MnO3 nanoparticles

We have reported here a new route to synthesize nanosized La0.75Ca0.25MnO3 perovskite crystalline complex oxides at a calcination temperature of 450‐6008C using the amorphous molecular alloy of La‐Ca‐Mn‐DTPA as precursors. The size and topography of the oxides are dependent on the calcinating temperature of the precursors. The resulting particle size is in a range of 20‐100 nm as determined by transmission electron microscopy. The magnetization of La0.75Ca0.25MnO3 nanophase is strikingly dependent on the particle size. The magnetoresistance of the samples shows spin-polarized tunneling behavior at low temperatures. q 2000 Elsevier Science Ltd. All rights reserved.

Enhanced magneto-optical Kerr effects and decreased Curie temperature in Co–Mn ferrite thin films

Co–Mn ferrite thin films were prepared on a monocrystalline silicon substrate by a sol–gel process, and the influences of Mn3+ on the microstructure, magnetism, and polar magneto-optical Kerr effects of the as-deposited films were examined. The results reveal that doping of Mn3+ ions could effectively lower the TC of Co ferrite, and the Mn3+ substitution caused enhanced Kerr rotations due to the migration of Co2+ from the octahedral site to the tetrahedral site. A maximum rotation of 2.7° was produced by the stress in the metastable cubic structure of CoFe0.6Mn1.4O4 films.

Fabrication and magnetic investigation of Y or Gd containing CoFe2O4 nanocrystalline films

The exertion for carrying out the substitution of Fe3+ ion in CoFe2O4 spinel by Y3+ and Gd3+ ions has been put forth in the present article. Y or Gd containing CoFe2O4 nanocrystalline films with average particles size of 65 nm were synthesized by sol-gel method, and then the magnetic properties of the products were investigated at room temperature. To improve the crystallization of Gd-doped cobalt spinels, we buffered them on about a 20-nm-thick CoFe2O4 thin film. However, the analysis on the results for both x-ray diffraction and magnetic measurement showed that it is difficult to perform the doping of Y3+ ions inside cobalt spinel ferrite. The proper doping amount of magnetic Gd3+ ion can enlarge saturation magnetization (Ms) and coercive force (Hc) of resultant nanocrystalline films, whereas the doping of Y only reduces them.