A Mn-Zn ferrite composed of 35.2 MnO, 9.8 ZnO and 55 $Fe_2O_3$ in mole percentage with or without an addition 0.06 wt% $CaCO_3$ and $V_2O_5$ was chosen to study the effect of variation in atmosphere at sintering and cooling stages on magnetic properties such as initial permeability and Q factor of the ferrite.
The maximum green and sintered density of a Mn-Zn ferrite was obtained when the powder was calcined at 925℃ in which 51% of the spinel phase was formed.
The apparent density and the initial permeability of the ferrite gradually decreased while the Q factor increased when the oxygen partial pressures were increased from 1 to 20% at sintering temperature of 1300℃. Such variation in the characteristics of the ferrite were discussed in terms of grain size, grain boundary effects, reduction-oxidation of iron ion and depletion of zinc ion in the structure.
The ferrite with an addition of CaO and $V_2O_5$ showed higher values in permeability and Q factor as compared with one without the additives.
The highest quality of Mn-Zn ferrite in terms of both permeability and Q factor was obtained by introducing a two-stage sintering process; that is, in the first stage of sintering up to 1300℃, a 20% of oxygen partial pressure was maintained, then converting into $N_2$ atmosphere at the second stage at the same temperature followed by controlling the equilibrium oxygen partial pressure from 1300℃ to 1000℃ on cooling. The ferrite thus obtained showed 3200 in μi and 13 in Q factor.
