1996 Volume 43 Issue 1 Pages 19-24
Today, Sr-ferrite and Ba-ferrite with hexagonal structure are widely used as permanent magnets. However, Ba-ferrite is considered to be unsuitable for high performance magnets compared with Srferrite because of its lower K1 value. In this study, submicron-sized Ba-ferrite powders were prepared to achieve higher corecivity. On the other hand, addition of SiO2 and CaCO3 (or CaO) is usually carried out to get high density and inhibit grain-growth during sintering. Without difficulty, it is predicted that Sr and Ba can be substituted for Ca, because they have similar characters. Therefore, in this study, addition of alkaline-earth elements and silica was investigated systematically. As a result, by addition of Si02-SrCO3 in Ba-ferrite, high performance Ba-ferrite magnets (Br=4.3kG, HcJ=3.6kOe) were obtained. At the same time, we discovered that they have equal shrinkage ratio in a-axis and c-axis. These unique results were due to the inhibition of grain-growth along a-axis. Furthermore, Ba segregation was found at grain boundaries besides Si and Sr by TEM-EDS analysis.
