SIGNATURE OF LINEAR (BULAEVSKII-GINZBURG) DOMAIN-WALLS NEAR T(C) OF BA-HEXAFERRITE

The domain wall dynamics of a BaFe12O19 single crystal has been studied by measurements of the linear ac susceptibility parallel to the easy axis between 10 and 10(6) Hz. In the temperature interval 0.98 T(c) less-than-or-equal-to T less-than-or-equal-to T(c) = 742.5 K, both dispersion and absorption reveal pure relaxational behavior, the damping rate GAMMA(W) of which exhibits a distinct minimum about T* = 0.992 T(c). Based on previous results on low-temperature ferromagnets (T(c) < 3 K) and recent theoretical work, the speeding up of GAMMA(W) approximately (T(c) - T)-0.7 toward T(c) is related to the relaxation of linear domain walls proposed by Bulaevskii and Ginzburg. For the first time, additional support for this wall type is gained from the magnitude of the wall-reconstructuring temperature T*. The steep rise of GAMMA(W) below T* can be related to Bloch-wall damping, however, the shape of the crossover of GAMMA(W) about T* remains to be explained.