The effect of dopants on the incremental permeability of MnZn-ferrites

In this paper the effect of some common grain boundary dopants, such as calcium oxide and niobium oxide, and of some processing parameters, on the incremental permeability of (Mn0.57Zn0.34Fe0.09)Fe2O4(Mn0.57Zn0.34Fe0.09)Fe2O4 ferrites in the temperature region of -40-40 to 85∘C is examined, in relation to the non-magnetic grain boundary models. Doped grain boundaries influence the incremental permeability in a different way than they influence the initial permeability, most probably because the dominating magnetization mechanism between those two properties changes. For the achievement of high incremental permeability, a shift of the hysteresis loop towards higher fields is essential. Besides the usage of grain boundary dopants, this can be more effectively achieved also with the usage of bulk dopants that dissolve into the lattice and induce high anisotropy and domain wall pinning, like cobalt. A 1500 ppm cobalt doped material is synthesized exhibiting initial permeability μi>4000μi>4000 and μΔ>2000μΔ>2000 over the entire temperature region from -40-40 to 85∘C.