Derang Cao

Nonmetal sulfur-doped coral-like cobalt ferrite nanoparticles with enhanced magnetic properties

We have successfully prepared a series of sulfur-doped cobalt ferrite nanoparticles via a facile and novel calcining process in air. The technique requires neither pH regulation nor a gas atmosphere nor centrifugation nor any other supplementary reagents during the preparation process. Our various characterizations confirmed that the nonmetal sulfur element was successfully doped in the cobalt ferrite nanoparticles. As the sulfur concentration was increased, the shapes of the sulfur-doped cobalt ferrite nanoparticles changed, from compact microspheres to sparse coral-like nanoparticles. Significantly, the saturation magnetization of sulfur-doped cobalt ferrites was measured to be as high as 81 emu g−1, which is particularly different from the decreased saturation magnetization of previously reported metal element doping.

A novel method to fabricate CoFe2O4/SrFe12O19 composite ferrite nanofibers with enhanced exchange coupling effect

Nanocomposite of CoFe2O4/SrFe12O19 has been synthesized by the electrospinning and calcination process. A novel method that cobalt powder was used to replace traditional cobalt salt in the precursor sol-gel for electrospinning was proposed. The crystal structures, morphologies, and magnetic properties of these samples have been characterized in detail. Moreover, when the average crystallite size of the hard/soft phases reached up to an optimal value, the CoFe2O4 have an enhanced saturation magnetization of 62.8 emu/g and a coercivity of 2,290 Oe. Significantly, the hysteresis loops for the nanocomposites show a single-phase magnetization behavior, and it has been found that the exchange coupling interaction strongly exists in the CoFe2O4/SrFe12O19 magnetic nanocomposite nanofibers.

Electrodeposition of FeCoCd films with in-plane uniaxial magnetic anisotropy for microwave applications

FeCoCd thin films with 500 nm thickness are directly prepared through electrodeposition in the sulphate bath in which glycine and citric acid were added as complex agents. The composition, structure, and magnetic of FeCoCd films were investigated as a function of Cd2+ concentration, cathode current density, and deposition temperature. A wonderful soft magnetic FeCoCd film was prepared and its coercivity of easy axis and hard axis are 5 Oe and 4 Oe, respectively. The natural resonance frequency is about 3.0 GHz, which imply that the FeCoCd film is potential candidate for high frequency applications.

A facile strategy for synthesis of spinel ferrite nano-granules and their potential applications

We have demonstrated a facile method to synthesize a number of spinel ferrite nano-granules in dimethyl formamide (DMF) through a calcination process under air. There is no pH regulation, gas atmosphere, centrifugation, supplementary reagents, or other complicated and cumbersome procedures during the preparing process. The structures, morphologies, and magnetic properties of NiFe2O4, CoFe2O4, and NiZnFe2O4 nano-granules in various DMF concentrations and different calcination temperatures were investigated systematically, and other MFe2O4 nano-granules were also investigated by this method. As a result, it will cause an impurity phase at low DMF concentration or low calcination temperature, and large quantities of uniform nano-granules will be achieved at about 680 °C in pure DMF. The results show that the method realizes a simple, rapid and convenient route for assembling unitary and binary spinel ferrite nano-granules. In addition, the formation mechanism of the nano-granules was also studied in detail, and DMF plays a dispersing and covering role during the reaction. This synthetic approach also shows great potentiality in the synthesis of maghemite γ-Fe2O3 with high saturation magnetization, and rare nonmetal-doped CoFe2O4 is prepared using this strategy. Magnetic properties of doped CoFe2O4 nano-granules are also improved. These results provide a convenient way for the advancement of magnetic nanomaterials.