Synthesis and Characterization of CoO, Co₃O₄, and Mixed Co/CoO Nanoparticules

Abstract

Very small nanometric oxide particles (CoO and Co 3 O 4 , around 2 nm in diameter) well dispersed inside a polymer matrix were prepared by solid-state oxidation of a metallic colloid precursor (1.6 nm Co particles). WAXS (wide-angle X-ray scattering) and HREM (highresolution electronic microscopy) were used to observe very precisely the structural changes occurring during the oxidation process. With cobalt particles a few nanometers large, air oxidation at room temperature results in a surface passivation. Consequently the particles show a composite structure with a metallic core surrounded by an oxide surface layer. Preliminary magnetic measurements reveal that unidirectional exchange anisotropy between the metallic ferromagnetic core and the antiferromagnetic oxide layer occurs below 130 K.

Monodispersed metal clusters in solid matrices: A new experimental setup

“…ZFC-FC curves were measured between 200 and 500Oe for all samples to avoid field effects. The shoulder at ∼ 175K was observed in all samples and is attributed to the blocking temperature of the Cobalt-oxide layer [27,28]. A clear difference between small and larger clusters den 6500 2300 600 15 T B > 300K 65K 20K 50K HC (3K) 600Oe 550Oe 330Oe 530Oe posited is observed:…”

In-Situ Reduction of Promoted Cobalt Oxide Supported on Alumina by Environmental Transmission Electron Microscopy

“…Recent TEM studies report on the observation of metallic cobalt nanoparticles regularly dispersed in a polymer matrix [22,23]. In these studies decomposition of organometallic precursors in the presence of a reactive gas produced metallic cobalt nanoparticles.…”

Exchange bias and vertical shift in CoFe2O4 nanoparticles

“…This is due to the large anisotropy of the AFM layer that prevents the AFM spin rotation and these in turn prevent the FM spins in turning away from the cooling direction. Furthermore, it has been shown [11,12] that the hysteresis loop may also show a vertical shift of the magnetization that is related to the presence of pinned interfacial spins. A positive (upward) shift is attributed to a ferromagnetic interface coupling and a negative shift for an antiferromagnetic interface coupling.…”