Self propagating high-temperature synthesis of chromium substituted magnesium zinc ferrites Mg_0.5Zn_0.5Fe_2–xCr_xO₄ (0≤x≤1.5)

Abstract

Magnesium ferrite MgFe₂O₄ and chromium substituted magnesium-zinc ferrite Mg_0.5Zn_0.5Fe_2–xCr_xO₄ (0≤x≥1.5) have been made in air by self-propagating high temperature synthesis (SHS), a combustion process involving the reaction of magnesium, zinc, iron(III) and chromium(III) oxides with iron or chromium metal powders and sodium perchlorate. This produced an orange-yellow propagation wave of velocity 2-3 mm s^–1. Two series of SHS samples were produced: series 1, SHS followed by annealing at 1400°C for 2 h and series 2, SHS in a magnetic field of 1.1 T followed by annealing at 1400C for 2 h. X-Ray data showed that in all cases nearly phase pure cubic spinel ferrites were produced. Changes in the cubic lattice parameter were seen as a function of Zn and Cr content. Room temperature and 80 K Mössbauer data showed a significant change in sublattice occupancy with Cr content. Magnetic hysteresis data for series 1 and 2 showed that the coercive force of doped samples is higher than pure compositions whilst magnetisation is lower. It was also shown that the use of a magnetic field during SHS can influence the microstructure and magnetic properties of the final material.

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