Study On The Synthesis Of Magnetic Nanoparticles With Tunable Sizes And Magnetic Properties Of Their Assembled Films

Assembled films from nanoparticles have received great concern for their potential applications in electronic,optoelectronic and magnetic divices.In recent years,the self-assembly of nanoparticles has developed from single component to binary component.Compared to the single-component assembled films,interparticle interactions presenting in binary component assembled films are more complicated with collective properties that are not simply the sum of individual nanoparticle properties,which is useful to broadenthe application of nanoparticles.Two types of nanoparticles(distinct in nature and sizes)are coassembled into assembled films with designated structures,which is one of effective ways to construct micro-electronic devices.An organic-solution method for the synthesis of monodisperse magnetic nanoparticles is presented in this thesis.In the reaction,Fe-oleate or Mn-oleate complex was used as precursor respectively,alkene as solvent and oleic acid as surfactant.Fe3O4 nanoparticles with mean diameters varying from 3 to 13 nm and MnO nanoparticles with average diameters ranging from 6 to 18 nm were obtained.Controllable sizes changing from 7 to 14 nm of Ni nanoparticles were obtained by using nickel(II)acetylacetonate as precursor,oleylamine as reducer and solvent,1,2-hexadecanediol and trioctylphosphine as surfactant.The results of reaction manifested that a decrease of precursor concentration to 0.1 mol/L or using mixed long-chain hydrocarbon as solvent willreducethe reaction temperature and the mean diameters and obtain a narrow particle size distribution.The increase of oleic acid concentration within 0.15 mol/L can raise the size and monodispersity of Fe3O4 and MnO nanoparticles at the same time.Besides,0.15 mol/L oleic acid contributed to gaining spherical MnO nanoparticles.On the basis of monodisperse magnetic nanoparticles synthesized above,we took solvent-vaporation method and spin-coating method to induce their self-assembly on the SiO2/Si wafer.In addition,self-assembly of Fe3O4-MnO or Fe3O4-Ni nanoparticles into assembled films were tentativelyattempted.From SEM observation of single-component,we found that most of the assembled films formed by solvent-vaporation method were multilayers in hcp stacking,while monolayers or multilayers were achieved with disordered arrays by spin-canting method.Finally,the study on magnetic characteristics of all the single or binary component assembled films was explored,which were prepared by spin-canting method.Almost all of assembled films formed by Fe3O4 or Ni nanoparticles showed superparamagnetic behavior at room temperature,and the blocking temperatures increase with increasing particle sizes.Last but not least,assembled films assembled from 8.7 nm Ni and 10.6 nm Fe3O4 with 1:3 particle ratio showed single-phase-like magnetic behavior,which indicated that there were interparticle dipolar interactions between two nanoparticle components in Ni-Fe3O4 assembled films to reduce its blocking temperature(TB)to 130 K,compared to that(137 K)of Fe3O4 assembled films.