Magnetic properties of CoFe1.9RE0.1O4 nanoparticles (RE=La, Ce, Nd, Sm, Eu, Gd, Tb, Ho) prepared in polyol

Abstract Highly crystalline CoFe 1.9 RE 0.1 O 4 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), 57 Fe 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 RE 3+ ions for Fe 3+ 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 CoFe 2 O 4 induced by the insertion of the relatively large RE 3+ ions. The low-temperature saturation magnetization and coercivity appear to be greatly affected by the nature of RE 3+ ions—maxima values were found for Gd 3+ and Eu 3+ , respectively.