Zn- and Cu-substituted Co2Y hexagonal ferrites: Sintering behavior and permeability

Y-type polycrystalline hexagonal ferrites Ba2Co2-x-yZnxCuyFe12O22 with 0 <= x <= 2 and 0 <= y <= 0.8 were prepared by the mixed-oxide route. Single phase Y-type ferrite powders were obtained after calcinations at 1000 degrees C. Samples sintered at 1200 degrees C show a permeability that increases with the substitution of Zn for Co and display maximum permeability of mu'=35 at 1 MHz for x = 1.6 and y = 0.4. A resonance frequency f(r) = 500 MHz is observed for Zn-rich ferrites with y = 0 and 0.4. The saturation magnetization increases with substitution of Zn for Co. Addition of Bi2O3 shifts the temperature of maximum shrinkage down to T <= 950 degrees C. Moreover, an increase of the Cu-concentration further lowers the sintering temperature to T <= 900 degrees C, enabling co-firing of the ferrites with Ag metallization for multilayer technologies. However, low-temperature firing reduces the permeability to mu' = 10 and the resonance frequency is shifted to 1 GHz. Thus substituted hexagonal Y-type ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications. (C) 2012 Elsevier B.V. All rights reserved.