Abstract
Highly crystalline CoFe1.9RE0.1O4 ferrite nanoparticles, where RE = La, Ce, Nd, Sm, Eu, Gd, Tb, and Ho, have been synthesized by forced hydrolysis in polyol. X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), Fe-57 Mossbauer spectrometry, Co K-edge X-ray absorption spectroscopy and magnetic measurements using a SQUID magnetometer were employed to investigate the effect of the substitution RE3+ ions for Fe3+ ones on the structure, the microstructure, the chemical homogeneity, and the magnetic properties of the cobalt ferrite system. All the produced particles are superparamagnetic at room temperature. Nevertheless, the substitution causes reduction of the blocking temperature which is mainly ascribed to partial cation exchange among the spinel-like sublattices of CoFe2O4 induced by the insertion of the relatively large RE3+ ions. The low-temperature saturation magnetization and coercivity appear to be greatly affected by the nature of RE3+ ions-maxima values were found for Gd3+ and Eu3+, respectively. (C) 2008 Elsevier B.V. All rights reserved.