Abstract: 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.

Key words: M-type hexaferrite with barium surplus, cell parameter, crystal shape transformation, magnetic properties