Synthesis and Exchange Bias in γ-Fe₂O₃/CoO and Reverse CoO/γ-Fe₂O₃ Binary Nanoparticles

Abstract

γ-Fe₂O₃/CoO and reverse CoO/γ-Fe₂O₃ binary nanoparticles have been prepared by a facile, two-step chemical route through the thermal decomposition of Co(acac)₂ and Fe(acac)₃ in hot oleyl amine. The synthesis is based on heterogeneous nucleation and growth of the second component on seed nanoparticles of the first one. The binary particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The heteroparticles are very stable in nonpolar organic solvents due the organic coating that is formed in situ. The presence of the antiferromagnetic CoO phase leads to unidirectional anisotropy, which is shown to originate from both magnetically compensated and uncompensated interfaces.