Bimagnetic CoO Core/CoFe₂O₄ Shell Nanoparticles: Synthesis and Magnetic Properties

Abstract

In this work we report on the synthesis, the microstructural characterization, and the magnetic properties of ∼7 nm bimagnetic core/shell nanoparticles prepared by seed-mediated growth high temperature decomposition of organometallic precursor. The nanoparticles are formed by an antiferromagnetic CoO core coated with ferromagnetic CoFe2O4 shell of 2–3 nm of thickness. XRD and electron diffraction patterns show the reflections of the structure of the CoFe2O4 and CoO phases and Dark- and Bright-field TEM images provide evidence of the core–shell morphology of the system. Magnetic measurements show that the system presents a remarkably large coercivity and high squareness (at 5 K, HC = 27.8 kOe and Mr/MS = 0.79), compared to CoFe2O4 single phase nanoparticles of comparable size. The enhancement of the effective anisotropy is attributed to the surface and interface exchange coupling effects.