Size and fluctuation effects on the dynamics of linear domain walls in an Ising ferromagnet

Approaching the Curie temperature of LiTbF₄ ellipsoids of thicknesses between 0.5 and 7 mm up to Tc-T=3×{}10^-4{T}c$, the first clear evidence for critical fluctuations and macroscopic size effects on the domain-wall relaxation is presented. An analog to the Landau-Lifshitz model proposed recently and additional optical data on the domain width suggest associating both phenomena with the existence of linear (Bulaevskii-Ginzburg) walls and with domain branching near the surface.