Without any surfactant, antiferromagnetic Co3O4 nanoparticles were synthesized successfully for the first time by means of an oxidation-reduction method with cobalt sulfate as starting material, which was oxidized to cobalt salt by NaNO3 after alkalinizing with NaOH. Morphological, structural, spectroscopic and magnetic characterization of the product were done by SEM, TEM, XRD, and VSM, respectively. The average crystallite size (on the base of line profile fitting method), D and σ, is estimated as 30 ± 6 nm. Some anomalous magnetic properties and their enhanced effect have been observed in Co3O4 antiferromagnetic nanocrystallites, including a bias field, coercivity, permanent magnetic moments and an open loop. These phenomena are attributed to the unidirectional anisotropy which is caused by the exchange coupling between AFM and FM layers, the existence of the spin glass like surface spins of Co3O4 nanoparticles due to size effects and surface-area effect. [...]
Water-soluble Mn3O4 nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn3O4 nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles. [...]
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