Anomalous viscosity and thermal remagnetization in Monte Carlo simulationsof planar random spin-models

A ferromagnetic, planar spin-model with random anisotropies in two dimensio ns is used to simulate thermally activated processes in exchange-coupled, t wo-phase permanent magnets by Monte Carlo dynamics. Simulations of hysteres is and slow relaxation processes at finite temperature are reported. The mo del displays exchange-spring behavior, anomalous viscosity along recoil loo ps, and thermal remagnetization in qualitative accord with experimental fin dings on spring magnets. The anomalous relaxation of the model can be expla ined by shrinking of subcritical interaction domains along the recoils, It is argued that disorder is important for the observability of anomalous vis cosity in materials, which undergo magnetic reversal by nucleation and grow th of interaction domains.