Synthesis, structure and magnetic properties of multipod-shaped cobalt ferrite nanocrystals

Abstract

We applied a general non-aqueous route for the formation of mono-, bi-, tri-, tetra, hexapod and multipod magnetic spinel ferrite metal oxide (CoFe₂O₄) nanocrystals. The magnetic CoFe₂O₄ nanocrystals were characterized by X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy, magnetometry and Mössbauer spectroscopy, to understand their structure and magnetic properties. These CoFe₂O₄ nanoparticles have the smallest particle size reported ever, with a mean diameter of ∼3 nm. The coercivity was found to be larger compared to that reported in the literature for spherical particles. Mössbauer spectroscopy indicated a magnetic transition above room temperature, where 20% of the Fe ions transit to a paramagnetic state, around 400 K. From the thermal dependence of magnetic parameters, the blocking temperature was estimated to be around 425 K. These studies indicate that our CoFe₂O₄ nanocrystals are different from their cubic/spherical counterparts, which generally display a single domain character. These CoFe₂O₄ nanocrystals display a strong shape anisotropy dependent magnetic property.