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 10⁴s 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 μs), 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.