Kinetic Aspects of Magnetic Relaxation in Amorphous Ferromagnetic Alloys

Abstract

Relaxation processes are a distinctive feature of metallic glasses. Their kinetics has been studied in great detail under very different conditions. In fact, owing to the intrinsic metastability of these materials, virtually all the measurable physical quantities are observed to relax. Relaxation processes in metallic glasses may be either irreversible or reversible, the former being essentially related to the structural relaxation of the substance towards an ideal equilibrium state pertaining to the considered temperature (in isothermal anneals), i.e., the undercooled liquid. Reversible processes are mainly related to changes in the so-called CSRO (compositional short-range order) of the alloy. The two processes often occur in similar temperature regions, and are most probably correlated. The kinetics of relaxation in metallic glasses is clearly nonexponential, indicating more than a simple Debye-type process. In several cases, the kinetics is of logarithmic type over some orders of magnitude of time. As a consequence, the popularity of a description in terms of a superposition of many exponential decays, with a suitable weighing function for the time constants, has always been high (1).