DOMAIN-WALL RELAXATION NEAR THE DISORDER TRANSITION OF BLOCH WALLS IN SR HEXAFERRITE

By measuring the linear ac susceptibility of single crystals of SrFe12O19 between 10 Hz and 20 MHz, the domain-wall dynamics have been investigated near the continuous phase transition from Bloch to linear walls at T*0.99TC. There the kinetic coefficient of the wall relaxation Lw has a deep minimum, the essential features of which indicate the presence of strong, two-dimensional Ising-like fluctuations of the order parameter of the Bloch walls. Magnetic fields, applied transverse to the easy c axis, increase Lw in almost quantitative agreement with predictions of the Landau-Lifshitz-Bloch approach for the mean-field region away from T*. Effects of fluctuations in the critical region of the disordered phase remain unexplained. © 1995 The American Physical Society.