Abnormal grain growth and magnetic loss in Mn-Zn ferrites containing CaO and SiO2

Grain growth behavior in correlation with magnetic loss has been investigated in Mn-Zn ferrites with the variation of additive content and particle size of the system. The powders of (Mn_0.76Zn_0.24O)_0.94(Fe₂O ₃)_1.06 composition and the average particle size of 0.94 μm and 1.93 μm are prepared by milling the calcined powder in an attritor. CaO and SiO₂ are chosen as the additives and their content is varied from 0-5 wt%, respectively. If has been found that the grain morphology and the magnetic loss are greatly dependent upon the amount of additives and the particle size of the system. There is an optimum content of the additives to produce normal grain structure and low magnetic loss. Under a sufficient driving force of the system (approximately, submicron-sized powders), the abnormal (duplex) grain structure is developed in the specimens with the additives in excess of the optimum value. The possible mechanism of such impurity-induced abnormal grain growth is explained from the observed faceted ferrite grains which has been known to have singular surface structure and their growth kinetics controlled by two-dimensional nucleation. It is suggested that the additives content along with particle size control is one of the important processing variables to obtain the low-loss Mn-Zn ferrites with fine and uniform grain structure