  The changes of magnetic properties upon heat treatment of a metastable
supersaturated solid solution processed by severe plastic deformation are
investigated by in-situ AC-hysteresis measurements. Data are analyzed in the
framework of dynamic loss theory, with correlative investigations of the
microstructural properties. The evolution of hysteresis upon annealing points
out that the single-phase supersaturated solid solution remains stable up to
400{\deg}C, then hindering of domain wall motion sets in at this temperature.
At 600{\deg}C, a multi phase microstructure is present, causing a significant
increase in coercivity.
