The influence of the grain boundary on the temperature coefficient of Ti-substituted telecommunication ferrites

The composition of the grain boundaries of MnZn ferrites has been determined by AES. In Ti-substituted MnZn ferrites, apart from a Ca,Si and Ti-rich layer of about 2 nm, a Ti gradient is found over a broader region in the grain. The Ti gradient influences the magnetic anisotropy and therefore the temperature dependence of the permeability. The result is a flattening of the permeability vs. temperature curve. The origin of the gradient in the grain boundaries is discussed involving a CaO-SiO2-MNO-TiO2kind of phase at the grain boundaries above 1200°c.