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 Ba1+xCoTiFe10O19+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 (Hc) and the remanent magnetization (σr) of Ba1+xCoTiFe10O19+x are significantly increased (△Hc=16.99kA·m-1,△σr=5.36A·m2·kg-1) while the specific saturation magnetization (σS) keep almost constant as the x increases in the range 0-0.05, and that σs,, Hc and σr 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 Ba1+xCoTiFe10O19+x is not destroyed in the x range 0-0.20; the α-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.