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Width-controlled M-type hexagonal strontium ferrite (SrFe12O19) nanoribbons with high saturation magnetization and superior coercivity synthesized by electrospinning.

Width-controlled M-type hexagonal SrFe12O19 nanoribbons were synthesized for the first time via polyvinylpyrrolidone (PVP) sol assisted electrospinning followed by heat treatment in air, and their chemical composition, microstructure and magnetic performance were investigated. Results demonstrated that as-obtained SrFe12O19 nanoribbons were well-crystallized with high purity. Each nanoribbon was self-assembled by abundant single-domain SrFe12O19 nanoparticles and was consecutive on structure and uniform on width. PVP in the spinning solution played a significant influence on the microstructure features of SrFe12O19 nanoribbons. With PVP concentration increasing, the ribbon-width was increased but the particle-size was reduced, which distributed on a same ribbon were more intensive, and then the ribbon-surface became flat. The room temperature magnetic performance investigation revealed that considerable large saturation magnetization (Ms) and coercivity (Hc) were obtained for all SrFe12O19 nanoribbons, and they increased with the ribbon-width broadening. The highest Ms of 67.9 emu·g−1 and Hc of 7.31 kOe were concurrently acquired for SrFe12O19 nanoribbons with the maximum ribbon-width. Finally, the Stoner-Wohlfarth curling model was suggested to dominate the magnetization reverse of SrFe12O19 nanoribbons. It is deeply expected that this work is capable of opening up a new insights into the architectural design of 1D magnetic materials and their further utilization.

High saturation magnetization of γ-Fe2O3 nano-particles by a facile one-step synthesis approach.

We have demonstrated the synthesis of γ-Fe2O3 nano-particles through a facile and novel calcination process in the air. There is no pH regulation, gas atmosphere, additive, centrifugation or other complicated procedures during the preparing process. A detailed formation process of the nano-particles is proposed, and DMF as a polar solvent may slower the reaction process of calcination. The structures, morphologies, and magnetic properties of γ-Fe2O3 nano-particles were investigated systematically, and the pure γ-Fe2O3 nano-particles obtained at 200 °C display uniform morphology good magnetic property. The saturation magnetization of obtained pure γ-Fe2O3 is about 74 emu/g, which is comparable with bulk material (76 emu/g) and larger than other results. In addition, the photocatalytic activity for degradation of methylene blue is also studied, which shows proper photocatalytic activity.

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.

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.

Investigation on the structures and magnetic properties of carbon or nitrogen doped cobalt ferrite nanoparticles

Carbon or nitrogen doped cobalt ferrite nanoparticles were synthesized in the air by a facile calcination process. X-ray diffraction, mapping, X-ray photoelectron spectroscopy, and mössbauer spectra results indicate that the nonmetal elements as the interstitial one are doped into cobalt ferrite nanoparticles. The morphologies of doped cobalt ferrite nanoparticles change from near-spherical to irregular cubelike shapes gradually with the increased carbon or nitrogen concentration, and their particles sizes also increase more than 200 nm. Furthermore, the saturation magnetization of carbon doped cobalt ferrite is improved. Although the saturation magnetization of N-doped cobalt ferrite is not enhanced obviously due to the involved hematite, they also do not drop drastically. The results reveal an approach to synthesize large scale ferrite nanoparticles, and improve the magnetic properties of ferrite nanoparticles, and also provide the potential candidates to synthesis co-doped functional magnetic materials.

Tuning high frequency magnetic properties and damping of FeGa, FeGaN and FeGaB thin films

A series of FeGa, FeGaN and FeGaB films with varied oblique angles were deposited by sputtering method on silicon substrates, respectively. The microstructure, soft magnetism, microwave properties, and damping factor for the films were investigated. The FeGa films showed a poor high frequency magnetic property due to the large stress itself. The grain size of FeGa films was reduced by the additional N element, while the structure of FeGa films was changed from the polycrystalline to amorphous phase by the involved B element. As a result, N content can effectively improve the magnetic softness of FeGa film, but their high frequency magnetic properties were still poor both when the N2/Ar flow rate ratio is 2% and 5% during the deposition. The additional B content significantly led to the excellent magnetic softness and the self-biased ferromagnetic resonance frequency of 1.83 GHz for FeGaB film. The dampings of FeGa films were adjusted by the additional N and B contents from 0.218 to 0.139 and 0.023, respec...