Investigation of Structure, Microstructure and Magnetic Properties of Nano-Crystalline Zn Ferrite Synthesized at High Temperature

Zinc ferrite nano-material was prepared by direct fusion of ZnO with Fe
in air. The morphological and structural properties of the system under study
were investigated by scanning electron microscope (SEM) and X-ray powder
diffraction (XRD) applying MAUD and Win-Fit programs. The X-ray studies
show the coexistence of two phases. The major phase (66.66%) was determined
to be the cubic spinel phase of ZnFe2O4 with average apparent crystallite size
of about 48.7 nm and 81.5 nm respectively for Dβ and DF, while the minor
phase of ZnO (33.33%) has hexagonal structure. The studied zinc ferrite
present a uniform microstructure in the form of spherical grains as given by
SEM. The type and density of defects as determined by electron spin resonance
(ESR) are free spins with density 3.92x1023 cm-3. The presence of the ZnO
phase may enhance the creation of Zn vacancies as surface defects that give
rise to free spins. The magnetic properties of the system were studied using a
vibrating sample magnetometer (VSM) at room temperature under a maximum
field of 20 KOe. The coerricivity (HC), approximate saturation magnetization
(Ms), remnant magnetization (Mr) and Curie temperature (TC) are determined.
The low value of Ms is attributed to the high value of annealing temperature
that allowed the formation of a better degree of crystallinity, i. e. smaller
degree of inversion which enhances the magnetization. Also the absence of
magnetic saturation at 20 KOe seems to be due to the effect of both the surface
spin disorder in nano regime and the magnetic moment bearing ZnO impurity
phase. The present magnetic investigations argue a ferrimagnetic character of
the system under study.