  Bloch lines are formed to reduce the magnetostatic energy generated by the
Bloch walls in uniaxial magnets. Recently, it is reported that Bloch lines play
important roles in the emergence and helicity reversal of magnetic bubbles in
Sc-substitute M-type hexaferrites
(BaFe$_{12-x-0.05}$Sc$_{x}$Mg$_{0.05}$O$_{19}$). Although Bloch lines have been
discussed on the basis of micromagnetic simulations, the detailed structure was
not observed directly. In this study, we investigated the microscopic
structures of Bloch lines in BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$
uniaxial magnets. Differential-phase contrast scanning transmission microscopy
(DPC-STEM) directly revealed that the edges of the Bloch walls were misaligned
in the Bloch lines of BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$. From the
micromagnetic simulations based on the Monte-Carlo technique, we showed that
the misaligned Bloch walls were caused by the dipole-dipole interactions in the
hexaferrite. Our results will help to understand the microstructures of Bloch
lines at nanometer scale.
