Intrinsic magnetic after effect

Specimens of the pseudobinary series, Dy(CO,Ni)(_2), were made in order to investigate the variation in the shape of the hysteresis loop across the series. A pulsed-field magnetometer was used to obtain oscillo grams of the loops and also to derive the ordering temperature and molecular moment for each specimen. Using this data, the variation of critical field with composition was explained and demonstrated by assuming the domain walls in those materials to be very narrow (of the order of ten atomic spacings) and to be intrinsically pinned. The applicability of the models of thermal activation and, at lower temperatures, tunnelling of the domain wall through the barrier, due to Taylor and also those proposed by Egami were tested by studying the variation of the initial part of the magnetisation curve (i.e., below the critical field at which the magnetisation increases abruptly) with field sweep rate, composition, and temperature. Measurements of the magnetisation rate, (^dM)/(^dt), were also taken to understand the variation of domain wall mobility with applied field and temperature and hence examine the applicability of Taylor's and Egami's models further.