Grain-size dependence of absorption characteristics of the electromagnetic wave absorbers of ferrite-SiO2 composites

Grain-size dependence of electromagnetic absorbing characteristics for composite materials made of Ni-Zn ferrite and SiO2 was investigated using SiO2 with various grain sizes (29 mum, 30 nm, 12 nm, and 7 nm). The absorption characteristics of ferrite composites using SiO2 with an average grain size of 30, 12, or 7 nm were improved compared with those of ferrite composites using SiO2 with an average grain size of 29 mum in the low-frequency region. Furthermore, the grain size dependence of the absorption characteristics for composite materials of Mn-Zn ferrite with an average grain size of 130 nm and SiO2 with an average grain size of 29 mum was investigated. The absorbing center frequency shifted to a higher frequency region than that of Mn-Zn ferrite. (C) 2004 Wiley Periodicals, Inc.