Kinetics of Annealing of Permalloy Films with Increasing Concentrations of Sulfur

Abstract

Zero-magnetostrictive films have been annealed isothermally at 60°, 75°, and 90°C in a hard-axis saturating field. The films contained up to 6 wt% of sulfur. The time dependence of the change in anisotropy indicated the presence of simultaneous processes affecting a portion of the total anisotropy. The average relaxation time was independent of sulfur content at a given temperature, but the fraction of the anisotropy involved was directly dependent on the sulfur concentration in the film and independent of temperature. The kinetic equation which described the results was (lnP/lnP∞) = 1−exp[−(t/τ)1/2]. This general form may be derived from the conventional pair reorientational model by making τ = f(t) to take into account the removal, during the annealing in the transverse field, of the effect of the active centers introduced by the sulfur. An activation energy of 0.74 eV was found for the processes affected by the sulfur. Stabilization, i.e., annealing in an easy-axis field at 150°C, made the annealing kinetics in the hard-axis field at the lower temperatures independent of the sulfur content. The changes in anisotropy with time in the hard-axis field after stabilization appeared to follow the same kinetic law as before stabilization, but the fraction of anisotropy involved was greatly reduced and the activation energy was reduced to ∼0.4 eV. It is suggested that the inclusion of sulfur in the film produces vacancies, defects, strain fields, and other structural defects which allow iron-atom pair reorientation to occur at the low temperatures studied. The stabilization treatment anneals out the imperfections.