Spark plasma sintering is a powerful method to produce fine grain dense ferrite at low temperature. However the process, usually conducted in neutral atmosphere in a carbon die, yields carbon surface deposition and the reduction of Fe~(3+) into Fe~(2+). It is shown that subsequent annealing in air can remove carbon and under some conditions produce complete oxidation of Fe~(2+) ions. Regular values of the resistivity and permittivity (resp., 1 MΩm, 13 ε_0) are recovered for most samples annealed at temperatures not higher than 750 °C. A relatively high value of the permeability (up to 240) and a high merit factor (μ_s x f_r > 5 GHz) have been achieved.
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