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

LIMA; WINKLER; TOBIA; TROIANI; ZYSLER; AGOSTINELLI; FIORANI

CHEMISTRY OF MATERIALS

AMER CHEMICAL SOC

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

0897-4756

ABSTRACT: 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 withferromagnetic CoFe2O4 shell of 2−3 nm of thickness. XRD and electrondiffraction patterns show the reflections of the structure of the CoFe2O4and CoO phases and Dark- and Bright-field TEM images provideevidence of the core−shell morphology of the system. Magneticmeasurements show that the system presents a remarkably largecoercivity and high squareness (at 5 K, HC = 27.8 kOe and Mr/MS =0.79), compared to CoFe2O4 single phase nanoparticles of comparablesize. The enhancement of the effective anisotropy is attributed to thesurface and interface exchange coupling effects.