Effect of cobalt substitution on magnetic properties of Ba4Ni2−xCoxFe36O60 hexaferrite.

Co-substituted U-type hexagonal ferrite bulks, with composition of Ba₄Ni_2−xCo_xFe₃₆O₆₀ (x=0.2, 0.4, 0.6, 0.8), were prepared by a conventional ceramic method. Saturation magnetization (4π<italic>M</italic>_s), coercivity (<italic>H</italic>_c), and Curie temperature (<italic>T</italic>_c) were investigated. Anisotropy constant (<italic>K</italic>₁) was calculated by fitting the magnetization curve (<italic>M</italic>-<italic>H</italic>) according to the law of approach to saturation, and anisotropy field (<italic>H</italic>_a) was calculated accordingly. The results reveal that all the samples possess the U-type hexagonal crystallographic structure. With increasing cobalt substitution content (x), the lattice parameters (<italic>a</italic> and <italic>c</italic>) almost remain the same owing to the similar radii of Ni²⁺ (0.72 Å) Co²⁺ (0.74 Å) ions. 4π<italic>M</italic>_s goes up, while <italic>H</italic>_c<italic>H</italic>_c shows an opposite trend. <italic>K</italic>₁ and <italic>H</italic>_a monotonously decrease resulting from that cobalt substitution weakens the <italic>c</italic>-axis orientation. Additionally, <italic>T</italic>_c increases from 467 °C to 484 °C. [ABSTRACT FROM AUTHOR]