钡过量非化学计量M型铁氧体的合成与表征

采用并加共沉淀工艺在900℃热处理2h的条件下合成了单相钡过量非化学计量M型铁氧体Ba_1+xCoTiFe₁₀O_19+x(x=0.00、0.05、0.10、0.15、0.20), 并用XRD、SEM、TEM和VSM表征了这种新的非化学计量M型铁氧体的结构和磁学特性. 结果表明: 当0c和剩余磁化强度σ_r均随x增大而显著增大(Δσ_r=5.36A·m^2·kg^-1, ΔH_c=16.99 kA·m^-1, 但比饱和磁化强度σ_s基本不变; 0.053+离子被稀释导致σ_s、H_c和σ_r均随x增大而持续降低. 同时证实钡过量并不会导致晶体对称性破坏, 02+离子分布于平行于a轴方向的大孔隙位?置, 不仅具有助熔剂作用, 而且对磁畴壁产生了钉扎效应.

Synthesis and Characterization of Novel Non-stbichiometric M-type Hexaferrite with a Certain Barium Surplus

Single-phase non-stoichiometric M-type hexaferrite with a certain barium surplus Ba_1+xCoTiFe₁₀O_19+x (x=0.00, 0.05, 0.10, 0.15, 0.20) was synthesized by calcining the precursors at 900℃ for 2h obtained with the co-dump coprecipitation process. Structural and magnetic properties of the new non-stoichiometric M-type hexaferrite were investigated with XRD, SEM, TEM, VSM. The results show that the coercive field (H_c) and the remanent magnetization (σ_r) of Ba_1+xCoTiFe₁₀O_19+x are significantly increased (Δ H_c=16.99kA·m^-1, Δσ_r=5.36A·m²·kg^-1) while the specific saturation magnetization (σ_s) keep almost constant as the x increases in the range 0～0.05, and that σ_s, H_c and σ_r all continuously decrease as the x increases in the range 0.05～0.20 since Fe³⁺ ions become diluted. At the same time, it is confirmed that the crystal symmetry of Ba_1+xCoTiFe₁₀O_19+x is not destroyed in the x range 0～0.20; the a-axis length is significantly increased as the x increase in the range 0～0.10 accompanying a small increase of the c-axis length, and that the a-axis length almost not change although the c-axis length stably increases as the x farther increases in the range 0.10～0.20. In addition, the phenomena of the growth of crystal grains and crystal shape transformation from plane form to uniaxial one were observed by a series of SEM and TEM images. These results imply that the excessive barium cations, which not only act as fluxing agent but also produce the pinning effect to magnetic domainwall, are distributed in large holes along a-axis orientation of M-type barium hexaferrite.