Structural, magnetic and Mössbauer studies on nickel‐zinc ferrites synthesized via a precipitation route

Polycrystalline Ni‐Zn ferrite, with a well‐defined composition, Ni 0.8 Zn 0.2 Fe 2 O 4 , synthesized by a low‐temperature method showed the formation of a cubic ferrite phase with a crystallite size of ∼15 nm and saturation magnetization of M s ≈ 44 emu/g at room temperature. When calcined at higher temperatures (up to 1200 °C) the magnetization increased continuously to M s ≈ 67 emu/g. To understand the magnetic nature of the cubic ferrite phase formed at a temperature as low as 80 °C, 57 Fe Mössbauer spectra were recorded for samples annealed at three different temperatures, without any external magnetic field, and with an external field of H ext = 5 T, at 4.2 K. The spectral parameters at room temperature, namely, isomer shift, quadrupole splitting and hyperfine field, confirmed the presence of ultrafine superparamagnetic crystallites of Ni‐Zn ferrite. The Mössbauer spectra at 4.2 K revealed spin relaxation effects resulting in very broad sextets, characteristic of ultrafine crystallites. The Mössbauer spectra recorded at 4.2 K and H ext = 5 T showed well‐resolved two‐sextet pattern with characteristic hyperfine interaction parameters of the cubic ferrite phase. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)