Mossbauer spectroscopy and x-ray diffraction study of (Cd, Zn) substituted mixed ferrites.

Abstract

The study of magnetic properties and structures of Zn and Cd substituted mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray diffraction on powdered samples at about 300 K. Two series of mixed ferrites, (Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0) were synthesized. In the former series the effect of simultaneous site dilution by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated and in the latter the effect of single site dilution by Zn or Cd is also studied. The Mossbauer spectra show that the compounds transform with increase in x from ordered to disordered magnetic states. Systematic decrease in the hyperfine fields indicating weakening of the magnetic coupling with an increase in x is observed. We report the presence of a cross over effect with respect to the hyperfine fields on A and B sites at low concentration of diamagnetic ions in the simultaneously diluted series. Both series of compounds show no significant changes in isomer shifts with x. Differences in the evolution of Fe atoms on A and B sites between Zn and Cd based compounds are observed. The results of our analysis show that Zn and Cd ions occupy both tetrahedral and octahedral sites. The spinel structure of the compounds studied in this work is confirmed by X-ray diffraction (XRD). The lattice parameters derived from XRD show systematic change with x consistent with Vergard's law. In Cd based samples an increase of the lattice parameter with x is explained on the basis of the size difference of the cations involved. However, an anomalous behavior of the lattice parameter is observed in Zn based samples. The average grain sizes of the samples were determined from the line width of the (311) XRD intensity lines using the Scherrer formula. These vary between 50 nm and 70 nm for all the samples except for Zn and Al substituted samples which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The porosity, x-ray and bulk densities of the samples are also presented.