Domain structure of hexaferrite BaFe$_{12}$O$_{19}$ near the curie temperature

The features of the structure of domain walls in hexaferrite BaFe$_{12}$O$_{19}$ have been studied near the Curie temperature $T_C$ = 724 K. The studies have been performed on the single-crystal samples in ac magnetic field with frequencies of 73 MHz and 71 MHz, and in dc magnetic field in the range 0–0.25 kOe. In BaFe$_{12}$O$_{19}$ at temperature $T_1$ = 716 K, the magnetic structure of domain walls is changed: the Bloch walls change into linear walls as temperature increases. The value of $\Delta T = T_C - T_1 \approx$ 8 K. The physical mechanism considered in this work and determining the difference of temperature ranges of existence a magnetically ordered state and the temperature range of existence of the Bloch domain walls agrees with the experimental results. Estimation of the criterion of the Bloch domain wall transition to a linear wall at $T_1$ = 716 K agrees with the obtained experimental data.