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Magnetocaloric materials with composition of Mn 1.3 Fe 0.65 P 0.5 Si 0.5 have been prepared by ball milling and solid-state reaction methods and consolidated using powder annealing, and conventional and spark plasma sintering. Magnetic and calorimetric measurements show remarkable differences upon first cooling, and slight differences on second and further coolings between the samples prepared by different synthesis routes. Further measurements using Hall probe imaging in high magnetic field have been also carried out. As-prepared samples have been cooled down just above the critical temperature, and the first phase transition has been induced by application of a magnetic field. Bulk samples show staircase isothermal magnetization curves whereas powders show smoother transition curves.

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Spark Plasma Sintering is a powerfal 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 reduction of F e 3+ into F e 2+ . It's shown that subsequent annealing in air can remove carbon and, under some conditions, produce complete oxidation of F e 2+ ions. Regular values of the resistivity and permittivity (resp. 1 MΩm, 13 ε 0 ) are recovered for most samples annealed not higher than 750• C. Relatively high value of the permeability (up to 240) and high merit factor (µ s × f r > 5 GHz) have been achieved.

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