The Preparation And Magnetism Of The Monodisperse Nanoparticles Of Manganese Oxides

Magnetic nanoparticles of transition metal oxides have gained enormous interest forapplications in various fields such as data storage, catalysis, and biomedical imaging.Especially nanocrystals of simple binary metal oxides like MnO, NiO, or CoO have servedas model systems for the detailed description of magnetic properties in the nanometerregime. In this thesis, our main studies focus on the system of the Mn-based dilutedmagnetic semiconductor. We prepare MnO nanoparticles and transition metal dopedsamples through thermal decomposition. The synthesis, characterization, magnetic andoptical properties of the MnO nanoparticles and transition metal doped samples wereinvestigated as follows.1. MnO nanoparticles with cubic phase were obtained by thermal decompositionsynthetic technique using acetyl acetone manganese as manganese source in a hightemperature chemical environment provided by o leylamine with high boiling point. Theexperimental results show that the particles size increase with the increasing of thereaction temperature. At the same time, the size distribution of the particles has beenimproved. But the phase structure of the MnO nanoparticles has been never changed. Theresults of the magnetic measurements show that MnO nanoparticles in the lowtemperature show superparamagnetism. This is mainly attributed to the coupling effectbetween ferromagnetic interaction produced by the surface effect of the MnOnanoparticles and the antiferromagnetic interaction produced by the inner structure ofMnO nanoparticles. The ferromagnetic interaction of the particles are discussed in termsof the presence of uncompensated spins on the crystal surface.2. Mn_1-xFe_xO nanoparticles were prepared by thermal decomposition technique usingManganese（III） Acetyllacetonate as manganese source and Iron（II） Acetylacetonate asIron source in a high temperature chemical environment provided by o leylamine withhigh boiling point. The synthesis, characterization, magnetic properties of the nanoparticles were investigated. The experimental results show that the particles sizedecrease with the increasing concentration of the doped Fe ion. At the same time, the sizedistribution of the particles has been changed. But the phase structure of the nanoparticlesremain unchanged. The main reason is enhancement of ferromagnetic interaction causedby the doped Fe ion. Agglomeration is caused by the enhancement of magnetic interactionamong particles. The results of the magnetic measurement show that c urie extrapolatedtemperature is elevated with the increase of doping concentration. Meanwhile the blocktemperature（TB） of the particles is as elevated. This indicated that antiferromagneticinteraction in the nanoparticles is weakened while ferromagnetic inte raction is enhancedbecause of the doped Fe ion.3. Finally, we calculated the forbidden bandwidth of MnO nanoparticles doped by Feion. And we try to analyse the results. The results shows that the forbidden bandwidth ofFe-doped MnO nanoparticles increase with the increase of doping concentration. Thisexplains that the absorption spectrum of particles is weakened.