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

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 CoFe 2 O 4 shell of 2–3 nm of thickness. XRD and electron diffraction patterns show the reflections of the structure of the CoFe 2 O 4 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, H C = 27.8 kOe and M r /M S = 0.79), compared to CoFe 2 O 4 single phase nanoparticles of comparable size. The enhancement of the effective anisotropy is attributed to the surface and interface exchange coupling effects.