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

ENIO LIMA JR.; E. WINKLER; D. TOBIA; H. E. TROIANI; ROBERTO D. ZYSLER; E. AGOSTINELLI; D. FIORANI

CHEMISTRY OF MATERIALS

AMER CHEMICAL SOC

Lugar: Washington; Año: 2012 vol. 24 p. 512 - 516

0897-4756

In this work we report on the synthesis, the microstructuralcharacterization, and the magnetic properties of ∼7 nmbimagnetic core/shell nanoparticles prepared by seed-mediated growthhigh temperature decomposition of organometallic precursor. Thenanoparticles 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 provideevidence 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.