Evidence for critical fluctuations in Bloch walls near their disordering temperature

The temperature variation of the relaxation rate ${\mathrm{\Gamma }}_{\mathit{w}}$ of the domain walls about their transition at T=${\mathit{T}}^{\mathrm{*}}$ from the Bloch to the linear Bulaevskii-Ginzburg structure has been investigated in the uniaxial ferrimagnet ${\mathrm{SrFe}}_{12}$ ${\mathrm{O}}_{19}$. The significant suppression of ${\mathit{T}}^{\mathrm{*}}$ below the mean-field approximation (MFA) value along with the speeding up of ${\mathrm{\Gamma }}_{\mathit{w}}$(T≤${\mathit{T}}^{\mathrm{*}}$), 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.