Chemical synthesis of monodispersed Co and CoPt magnetic nanoparticles

Abstract

Size controlled synthesis of cobalt nanoparticles and their magnetic properties have been studied using organometallic precursors. The dicobalt octacarbonyl precursor is thermally decomposed in the presence of the alkyl sulfonate or alkyl ammonium bromide in toluene solution. Obtained Co nanoparticles from 2 nm to 25 nm have size variation with narrow size distribution (σ ＜ 10%). The X-ray diffraction (XRD) and electron diffraction (ED) pattern reveal that the cobalt nanoparticles have face-centered cubic structures. 2D and 3D structure of Co nanoparticles assembled on various flat substrates. Co nanocrystal superlattices (NCS) are the face centered cubic assembly and their interparticle distance is 10.3 nm and superlattice constant is 17.8 nm by TEM and small angle electron diffraction analysis. In magnetic properties, blocking temperature and magnetic coercivity are dependent on particle size. Blocking temperature is change from 10 K to over room temperature. Magnetic coercivity increases as increasing their size until 8 nm and decreases on the bigger particles. Core-shell and alloy structure of CoPt nanoparticles were synthesized from organometallic precursors and confirmed by HRTEM analysis. Magnetic property of $Co_{core}-Pt_{shell}$ nanoparticles is comparable to that similar size Co nanoparticles. However, CoPt alloy was enhanced compared to Co nanoparticles. Magnetic coercivity increased to 6900 Oe. In this thesis, the synthesis of Co, $Co_{core}-Pt_{shell}$ and CoPt alloy nanoparticles, formation of Co nanocrystal superlattices and their magnetic properties have been investigated