Synthesis and characterization of nanocrystalline RE-substituted (RE=La, Ce, Gd, Dy, Er, Yb) Mn-Zn ferrites

Nanocrystalline ferrites Mn$_{0.6}$Zn$_{0.4}$Fe$_{2y}$RE$_{y}$O$_{4}$ (RE=La, Ce, Gd, Dy, Er, Yb; y=0; 0.1; 0.2; 0.3) were synthesized by chemical co-precipitation method. The formation of FCC spinel structure and absence of impurity phases within each of the sample was confirmed by X-ray diffraction analysis. The cationic distribution within ferrites was obtained by atomic emission spectroscopy. Mean particle size calculated by Scherrer's formula from XRD data of dried powders ($\sim $10 nm) is in good agreement with one showed by transmission electron microscopy of the initially obtained particles in a diluted aqueous solution. Scanning electron microscopy confirmed the nanocrystalline morphology of the dried ferrite powders. Magnetic measurements in a temperature range 4 -- 393 K showed a typical superparamagnetic behavior, like non-hysteretic M(H) curves and a blocking temperature on M(T) dependencies. Infrared transmission spectra have been investigated in a range 40-3500 cm$^{-1}$. All spectra show a typical for cubic spinel lattice double peak in far IR, corresponding to the stretch-type vibrations on Me-O bonds in octahedral and tetrahedral sublattices.