Preparation and characterization of nanosize Mn-Zn ferrite

Synthesis of nanosize (9-12 nm) Mn0.65Zn0.35Fe2O4 particles from metal chloride solution through a hydrothermal precipitation route using aqueous ammonia, and their characterization by XRD, TEM and VSM are reported. Chloride ion concentration in the solution and the pH of precipitation are shown to play a crucial role in retaining the initial stoichiometry of the solution in the nanoparticles. While at lower pH, precipitation of Mn was incomplete, higher pH of precipitation led to Zn loss in the particles. The optimum pH for stoichiometric precipitation was found to lie around 10. The coercive force, H-c and the transition temperature, T-c (from ferrimagnetic to paramagnetic state) were highs compared to reported bulk values and confirm the nanosize nature of the particles. The M versus T curve, instead of showing a monotonic drop of magnetization, showed a cusp before T-c. This cusp-like feature is shown to arise due to an irreversible phase transition involving cationic redistribution in the unit cell of the nanoparticles. (C) 1999 Elsevier Science B.V. All rights reserved.