  Yb-substituted Ni-Zn ferrites have been synthesized using sol-gel auto
combustion method. The structural characterization of the compositions has been
performed by X-ray diffraction analysis, field emission scanning electron
microscopy (FESEM), quantum design physical properties measurement system
(PPMS). That ensured the formation of single phase cubic spinel structure.
Crystallite and average grain size are calculated and found to decrease with
increasing Yb3+ contents. Saturation magnetization and Bohr magnetic moment
decrease while the coercivity increases with the increase in Yb3+ contents
successfully explained by the Neels collinear two sub-lattice model and
critical size effect, respectively. Critical particle size has been estimated
at 6.4 nm, the transition point between single domain regime (below the
critical size) and multi-domain regime (beyond the critical size). Curie
temperature reduces due to the weakening of A-O-B super exchange interaction
and redistribution of cations, confirmed by the M-T graph. The compositions
retain ferromagnetic ordered structured below Curie temperature and above Curie
temperature, it becomes paramagnetic, making them plausible candidates for high
temperature magnetic device applications. The relative quality factor peak is
obtained at a very high frequency, indicating the compositions could also be
applicable for high frequency magnetic device applications.
