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We have characterized a system of maghemite, γ -Fe 2 O 3 , nanosized particles prepared by a microemulsion method using an ionic surfactant. The Mössbauer spectra from 21 to 298 K evolve from a totally magnetically split signal at low temperatures to a single superparamagnetic (sp) doublet at 298 K with a blocking temperature of ≈150 K. The real component of the AC susceptibility (5 ν 10 4 Hz) displays a behavior characteristic of a system of interacting particles. A broad distribution of the particle sizes is revealed by the much higher average energy barrier obtained by AC susceptibility than Mössbauer.

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The preparation of massive oxides Zn 1 − x Fe x O by means of mechanical milling in diverse gaseous atmospheres and starting with different powder mixtures was investigated. ZnO powder with 10 at.% admixture of Fe, FeO or Fe 2 O 3 , were milled during 1, 4 or 16 h and characterized by X-ray diffraction and Mössbauer spectroscopy. Different phases were obtained according to the initial conditions (precursor used, atmosphere, etc.) and phase's formation enthalpies.