Domain-wall dynamics in aligned bound Sm2Fe17

Abstract

ac susceptibility (?ac=??-j??) of an aligned bound Sm2Fe17 powder sample has been measured along the easy direction as a function of temperature, frequency, warming rate, and time. Anomalous behavior has been found in that with increasing temperature, ?? and ?? increase steadily up to T~150 K where a drop occurs. At higher temperatures ?? increases again, following an S-shaped curve which is accompanied by a ?? peak. Using a model two-level system for a thermally activated magnetic aftereffect process, ?=?0exp(Q/kT), the high-T ?? rise is explained by dynamic wall pinning and depinning owing to local directional ordering around domain walls with Q?0.53 eV and ?0?1.7?10-13 s. The low-T ?? peak is a consequence of domain-structure reconstruction and involves a long-range thermally hysteretic pseudostatic wall pinning and depinning process with average Q?0.42 eV and ?0?10-10 s. The reasons for the anomalies in ?ac(T) often found in rare-earth?transition-metal alloys are extensively discussed.