Synthesis of nanosize (9-12 nm) Mn0.65Zn0.35Fe2O4 particles from metal chlo
ride solution through a hydrothermal precipitation route using aqueous ammo
nia, 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 p
H for stoichiometric precipitation was found to lie around 10. The coercive
force, H-c and the transition temperature, T-c (from ferrimagnetic to para
magnetic 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-lik
e feature is shown to arise due to an irreversible phase transition involvi
ng cationic redistribution in the unit cell of the nanoparticles. (C) 1999
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