Evidence for critical fluctuations in Bloch walls near their disordering temperature

The temperature variation of the relaxation rate Γw of the domain walls about their transition at T=T* from the Bloch to the linear Bulaevskii-Ginzburg structure has been investigated in the uniaxial ferrimagnet SrFe₁₂{O}₁₉$. The significant suppression of ${T}*$ below the mean-field approximation (MFA) value along with the speeding up of ${{{Γ}}}w(T≤{T}*$), which is much stronger than that predicted by the MFA, reveals the first evidence for critical fluctuations in a domain wall. The speeding up can be almost quantitatively explained by taking two dimensional fluctuations of the transverse magnetization in the wall into account.