SLOW RELAXATION IN MAGNETIC-MATERIALS

Magnetic aftereffects in magnetic materials have previously been attributed to rotation of individual domains and wall motion between domains. We have measured the relaxation of the remanent magnetization as a function of time, in several magnetic materials including random magnetic systems and single-crystal ferromagnets, from 10(-5) to 10(4) s after removing an applied field. The observed behavior is accurately described by a thermodynamic model for the relaxation of finite-sized dispersive excitations (magnons) on specific distributions of dynamically correlated domains. At low fields (H < 10 Oe) and long times (t > 10 mus), aftereffects in magnetic materials are dominated by the relaxation of magnons on finite-sized domains. At higher fields, in addition to the low-energy magnon relaxation, single-crystal iron exhibits evidence for wall motion, which usually occurs on very short time-scales.