The role of internal and external demagnetizing effects in nanocrystalline alloys

Initial permeability measurements as a function of temperature have been carried out for toroidal and ribbon samples of both families of soft magnetic nanocrystalline alloys, Finemet and Nanoperm, varying the fraction of the crystalline phase by the annealing temperature. The shape of the curves for open flux circuit before and after T_c ^am has been explained taking into account the external and internal demagnetizing effects, respectively. For Finemet, an almost constant T_c^am has been obtained, while for the Nanoperm a steady increase of it from the as cast 70°C to 370°C as a function of annealing temperature has been measured. The latter result is in agreement with the recently published Mossbauer data and our hysteresis measurements