Synthesis and Magnetic Properties of Non-Stoichiometric ${\rm Co}_{2}{\rm Z}$ Hexaferrite

A several of non-stoichiometric Co₂Z hexaferrites with composition of Ba_3(1+x)Co₂Fe₂₄O_39+x (x = -0.20 - 0.20) have been synthesized. Their structural and magnetic properties have been characterized. It is found that the increase of Ba²⁺ amount is beneficial to the formation of Z-type phase and the reduction of sintering temperature. Excess Ba²⁺ ions distributed in the large interspace along a-axis orientation enhance the grain growth and densification due to the activation of lattice, which in turn first lead to an increase and then a decrease of saturation magnetization. Meanwhile, owing to the compact and uniform microstructures, and high sintering density, relatively high initial permeability was obtained in the samples with proper Ba²⁺ amount while magnetic loss no significant change. On the contrary, when x <; 0, the Z-type crystal structure of B₂S₄B₁S₄)₂ becomes unstable because of Ba²⁺ deficiency. The impurity phase was detected in these samples. Saturation magnetization decreases and coercive force increase with Ba²⁺ deficiency. Consequently, the initial permeability decreases.