Spin fluctuations of Fe³⁺ ions in cobalt–zinc ferrites using the Mossbauer effect

Abstract

Resonance absorption spectra of Fe⁵⁷ in Co_xZn_1-xFe₂O₄ (for x = 0.3, 0.5, and 0.75), in the temperature range from 80 to 700 °K, are discussed. The modulated lineshapes of the magnetic hyperfine spectra show features which are characteristic of relaxation effects. The theoretical line shapes, computed using the stochastic model, show good agreement with the experimental data at all temperatures for all the three compositions. For each composition, the relaxation time decreases very slowly with increase in the temperature, up to the magnetic transition temperature. Near the Neel temperature, the relaxation time starts decreasing rapidly, leading to the total collapse of the magnetic hyperfine splitting. The introduction of the Zn²⁺ ions in the ferrite increases the relaxation times at low temperatures (T < T_N). The change is, however, negligible for the increase in the Zn²⁺ concentration from x=0.5 to 0.3. This behaviour can be attributed to the role of Zn²⁺ ions in increasing the magnetic disorder in the ferrite. The increase in the concentration of Zn²⁺ ions causes the damping of the collective modes existing in an ordered ferrimagnetic system.