DOMAIN-WALL DYNAMICS IN ALIGNED BOUND SM2FE17

ac susceptibility (chi(ac) = chi' - j chi '') of an aligned bound Sm2F e17 powder sample has been measured along the easy direction as a func tion of temperature, frequency, warning rate, and time. Anomalous beha vior has been found in that with increasing temperature, chi' and chi '' increase steadily up to T similar to 150 K where a drop occurs. At higher temperatures chi' increases again, following an S-shaped curve which is accompained by a chi '' peak. Using a model two-level system for a thermally activated magnetic aftereffect process, tau-tau(Q)exp( Q/kT), the high-T chi' rise is explained by dynamic wall pinning and d epinning owing to local directional ordering around domain walls with Q approximate to 0.53 eV and tau(0) approximate to 1.7 x 10(-13) s. Th e low-T chi' peak is a consequence of domain-structure reconstruction and involves a long-range thermally hysteretic pseudostatic wall pinni ng and depinning process with average Q approximate to 0.42 eV and tau (0) approximate to 10(-10) s. The reasons for the anomalies in chi(ac) (T) often found in rare-earth-transition-metal alloys are extensively discussed.