High permeability-high frequency stable MnZn ferrites

Modern MnZn ferrite applications require high magnetic initial permeability and exceptional frequency stability; the former implies large grains, while the latter high grain boundary resistivity. In this article the optimization of the final firing process is described for achieving both. The optimization is based on the homogeneous dissolution of dopants under oxidative conditions and their subsequent precipitation along grain boundaries. This was accomplished by integrating isothermal plateaus at the upper stadia of the cooling stage of the final firing process. MnZn ferrites of the basic composition [Mn0.47Zn0.47Fe0.062+]Fe23+O4 were synthesized with initial permeability (measured at f=10 kHz, B < 0.1 mT, T=25 degrees C) 12,600 and losses, expressed as tan(delta)/mu(i), of 3.1 x 10(-6) at 10 kHz and 20.5 x 10(-6) at 100 kHz (B < 0.1 mT, T=25 degrees C), that reflect good frequency stability. These results could be reproduced in pilot production scale. (C) 2012 Elsevier B.V. All rights reserved.