EPR STUDY OF NANOSTRUCTURED ZINC FERRITE

Abstract

Bulk zinc ferrite has been studied in the past. In the bulk form zinc ferrite crystallizes in the normal spinel structure with all the zinc ions occupying the tetrahedral and all the iron occupying the octahedral sites, respectively. But, nanosize zinc ferrite is believed to crystallize in a different way. It is now well established that in a nanosize zinc ferrite there is partial inversion in the cation occupancy, leading to some kind of magnetic ordering in this system much above its Neel temperature of 10 K. Hence, there is ample scope of maneuvering the electrical and magnetic properties of this ferrite. In the present study nanosize zinc ferrite was prepared by a chemical reaction involving the nitrates of Zn and Fe and using the citric acid as the host. The sintering of the precursor was done for 1 h at various temperatures ranging from 300°C to 1000°C. These samples were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR). The average particle sizes in these sintered samples measured by TEM are found to vary from ≈ 10 to 62 nm. The XRD measurements show the formation of single-phase spinel structure in all the samples. The X-band EPR spectrum of the precursor specimen at room temperature consists of two EPR signals: an intense signal at g eff = 2.02 having peak-to-peak line width △H PP = 425 Gauss and other a weak signal at g eff = 4.51 having an asymmetric line shape. As the samples are heat-treated at different temperatures, the EPR signal corresponding to the intense peak gets stabilized at g eff ≈ 2.03, whereas the weak signal gets suppressed progressively. The spin–spin relaxation time in these samples have values ≈ 3 × 10-10 s . The effect of sintering temperature on the properties of the nanostructured specimen of zinc ferrite and the underlying mechanism would be discussed.