The Magnetic Properties And Hydrophobic Of Different Sizes Magnetite Nanoparticles

This dissertation reported some results of the different size magnetic nanoparticlesproperties.1.Magnetic measurements up to1000K have been performed on hydrothermallysynthesized a-Fe₂O₃nanoparticles （60nm） using a Quantum Design vibrating samplemagnetometer. A high vacuum environment （1×10-5Torr） during the magnetic measurementup to1000K leads to reduction of a-Fe₂O₃to Fe₃O₄. This precludes the determination of theNe′el temperature for the a-Fe₂O₃nanoparticles. In contrast, coating a-Fe₂O₃nanoparticleswith SiO₂stabilizes the a-Fe₂O₃phase up to930K, which allows us to determine the Ne′eltemperature of the a-Fe₂O₃nanoparticles for the frst time. he e′el temperature of the60-nm a-Fe₂O₃nanoparticles is found to be945K, about15K below the bulk value. The smallreduction of the Ne′el temperature of the a-Fe₂O₃nanoparticles is consistent with a fnite-sizescaling theory.2. We examine size-dependent structural and magnetic properties of fine size controllediron oxide nanoparticles in the4-17nm range using X-ray diffraction, Transmission ElectronMicroscopy （TEM）, M ssbauer and Quantum Design vibrating sample magnetometer. Fe₃O₄nanoparticle samples were prepared by the chemical method. XRD results confirmed thesamples to be nanostructured Fe₃O₄and indicated the particles size. hrough ssbauerspectra of various sized Fe₃O₄particles, we found that the ratio of Fe3+/Fe+2.5and the Fevacancies on the B sites can be modified by varying the particle size. Coating Fe₃O₄nanoparticles with SiO₂effectively eliminates magnetic interparticle interactions so that theCurie temperature （Tc） can be well fitted by an expression for noninteracting randomlyoriented single-domain nanoparticles. The Curie temperature of the samples was746K to849K lower than that of the bulk material, which may be related to a nanequilibrium cationdistribution. The results are discussed in terms of interparticle interactions induced by thethermal fuctuations, cation distribution, and other imperfections that exert fields proportionalto the particle size.3. We report high-temperature magnetic measurements of silica-coated nickelnanoparticles. The Curie temperature is found to decrease with decreasing particle size andfollow a fnite-size scaling relation with the correlation length exponent ν=1.06±0.07. hemeasured exponent is in excellent agreement with the reported values for nickel nanowiresand some nickel thin flms. he intrinsic ν value together with the experimental values ofother critical exponents consistently shows that the three-dimensional Heisenberg model is suffcient to describe the ferromagnetism of nickel.4. We successfully synthesized4-17nm Fe₃O₄magnetic nanoparticles with dual function,as both magnetic and the hydrophobic properties. We measured the magnetic, hydrophobicproperties of the different size nanoparticles. We observe that the magnetic and hydrophpbicproperties are sensitive to the particle size, such as the saturation magnetization （M_s） and thecontact angle （CA） of the sample increasing with the increase of the particle size. Moreover,we further got magnetic liquid marble coating a water droplet with highly hydrophobic Fe₃O₄nanoparticles through a mechanical method. We have found that the magnetic liquid marbleshave dual function, as both the force mediator and the hydrophobic-coating phase under theaction of a magnetic field. Such a magnet-induced temporary super-hydrophobic coating mayhave wide applications in electronic, biomedical, and defense-related areas.