Large Motions of the Magnetization in Magnetically Ordered Media

摘要

Two topics: (1) Interaction of domain wall motion with elementary excitations,and the resulting damping and instability mechanisms. The limiting wall velocity is very nearly equal to the speed of the particular spin wave whose group and phase velocities are equal. When the driving field is large enough to induce this limiting velocity, the system achieves a fixed point, a state in which a group of non-synchronous spin-waves is excited to a high, non-thermal level. (2) Self-organized criticality. Some further consolidation of this concept for large magnetic systems are achieved. Then, studies were begun to establish the minimum complexity a physical system must have if S.O.C. behavior is to result. Even though the concept appears to be very successful in at least two well-defined areas (earthquake statistics, and large, magnetically ordered systems) the reasons are unclear. The simplest algorithms used in their description assume that the systems get stuck in only just metastable states, but do not explain why.