Preparation And Characterization Of Soft Magnetic NiFe₂O₄-based Core-Shell Nanocomposite Particles

As an important soft magnetic material with high permeability and low hysteresis loss,NiFe2O4 have shown great potential in electronics industry such as head materials,moment magnetic materials,magnetic switch,and so on.Recently,considerable efforts have been dedicated to the design and preparation of core-shell structure particles consisting of NiFe2O4 and the other different chemical composition.The advantages of core-shell materials are derived from the properties(mechanical,optical,electrical,magnetic and catalytic)of core or shell can be tailored by their morphology component and structure of their shells or cores,which are different from individual NiFe2O4 particles.Therefore,considerable attentions have been devoted to the fabrication of core-shell soft magnetic nanocomposite materials.In this paper,both NiFe2O4/SiO2 and NiFe/NiFe2O4 were core-shell nanocomposite.The structure and properties of synthetic composites were characterized by using modern physical and chemical techniques,such as X-ray diffraction(XRD),Fourier transformation infrared spectra(FT-IR),scanning electron micrograph(SEM),transmission electron microscopy(TEM)and vibration sample magnetometer(VSM).The nanocrystalline soft magnetic NiFe2O4 as seeds in the polyethylene glycol octylphenyl ether(Triton X-100)/hexanol/cyclohexane/water microemulsion system,uniform nanoparticles consisting of a magnetic core of nickel ferrite(NiFe2O4)and a shell of silica(Si02)were successfully prepared by reverse microemulsion method.Studies showed that the magnetic crystal particles of NiFe2O4 had become complete when the calcination temperature was 600 ?.And the size of core was 18 nm,while saturation magnetization was 22.802 emu/g.With the increasing of TEOS concentration,Si02 layer thickness gradually increased,while the saturation magnetizations reduced gradually.On the other hand,remanence and coercivity of samples were close to zero,indicating that nanocomposites remain superparamagnetic after coated with SiO2.The potential mechanism of NiFe2O4/SiO2 core-shell nanocomposite particles was proposed:The ultrasonic irradiation promotes the formation of Si02 shell.This promotion arises from acoustic cavitations,that is,the formation,growth,and implosive collapse of bubbles in a liquid.When TEOS was added,it began to hydrolyze on the surface of ferrite nanoparticles.With the help of ultrasonic irradiation,the core-shell nanacomposites NiFe2O4/SiO2 were obtained.Nickel nanoparticles were coated ferric oxide by chemical precipitation method,Bimagnetic core-shell NiFe/NiFe2O4 nanocomposites were prepared in ultrasonic-assisted technology combined H2 reduction method.The results showed that:Ni/Fe2O3 nanocomposites had been reduced to core-shell nanocomposite NiFe/NiFe2O4 at 723 K.The average particle size of NiFe/NiFe2O4 nanocomposites was ca.100 nm.The nanocomposites exhibited paramagnetic properties with a total magnetization value of 29.9 emu·g-1.