High-Frequency Magnetic Properties of Ca-Substituted Co2Z and Co2W Barium Hexaferrite Composites

Abstract

A series of Ca-substituted Z-type hexaferrites having nominal composition Ba3– x Ca x Co2Fe24O41 ( $x = 0$ –1.5) was studied for their high-frequency magnetic properties, including measurement of the permeability spectra and magnetic loss over a frequency range of 0.1–10 GHz. Analyses of crystal composition and microstructure reveal that hexaferrite composites consist of the Z-type phase and increasing amounts of the W-type phase were obtained as the Ca content was increased. Correspondingly, the permeability $\mu ^\prime $ displays a near linear decrease with x varying from 0 to 1.5, from ~8 to ~4.1 at 0.1 GHz. The relationship between permeability and variations in intrinsic magnetic parameters, i.e., saturation magnetization $M_{s}$ and coercivity $H_{c}$ , follows the Globus model. Compared with the undoped Z-type hexaferrite, the sample with $x = 0.2$ has lower magnetic loss over a broad frequency range, and higher levels of Ca substitutions ( ${x} \ge 1$ ) lead to low magnetic loss at high frequencies. The dual-phase composite of Co2Z and Co2W in proper ratio is an effective technique to improve the homogeneity of grain and microstructure, and thus reduce the high-frequency magnetic loss of the sintering hexaferrites.