Microstructure and magnetic characteristics of low-temperature-fired modified Z-type hexaferrite with Bi/sub 2/O/sub 3/ additive

We have investigated the effect of Bi/sub 2/O/sub 3/ additive on the densification, low-temperature firing, and magnetic characteristics of modified Z-type Ba/sub 3/Co/sub 2/(1-x-y)Zn/sub 2x/Cu/sub 2y/Fe/sub 23.5/O/sub 41/ hexaferrite. Our results show that Bi/sub 2/O/sub 3/ additive not only improves the densification and promote the firing of modified Z-type hexaferrite prepared by the dry gel self-propagating method below 900/spl deg/C, but can also improve the magnetic properties. The average values of basic magnetic parameters of the hexaferrites with a small amount of Bi/sub 2/O/sub 3/ additive are stable: 50.0 emu/g saturation magnetization, 6.0 emu/g residual magnetization, 50 to 90 Oe coercive force, and 380 K Curie temperature. However, the main magnetic properties of low-fired hexaferrites are improved in that they attain an initial permeability of 4.0, a quality factor in excess of 50, a cutoff frequency greater than 1.0 GHz, and a dc resistivity of 3.30/spl times/10/sup 7/ /spl Omega//spl middot/cm. We discuss the relative mechanisms and factors involved in generating these effects in this paper.