Magnetic Properties and Annealing Behavior of Electrodeposited NiFeS Thin Films

Zero magnetostrictive films of FeNi with sulfur contents up to ∼6.5% by weight were prepared by electrodeposition from electrolytes containing thiourea. The total sulfur content in the films increased linearly with thiourea coacentration. The H_c varied from about 10 Oe for no thiourea, down through a broad minimum of about 4 Oe at intermediate thiourea concentrations. The dispersion α₉₀ also went through a broad minimum in this range; values as low as 1° were obtained. H_k was constant at 2.95±0.1 Oe above ∼1% sulfur. The effects of thiourea on H_c, H_k, and α₉₀ are interpreted in terms of its influence on crystallite size and shape, on the smoothness of the film, on the impurity content, and on the planar stresses in the film. With this electrolyte, film compositions were constant throughout their thickness to ±0.2% Ni. Exposure of these films to 60°C in a saturating field parallel to their easy axis produced no changes in H_c, H_k, or α₉₀ for times up to 2000 min. In a transverse field, the change in properties depended on the sulfur content of the films; the change in H_k with time followed $$\ln {\mathrm{(H}}_k^t{\mathrm{-H}}_k^{\infty }{\mathrm{)/(H}}_k{\mathrm{-H}}_k^{\infty }{\mathrm{)=-(t/\tau )}}^{\text{1/2}}$$ out to 6000 min, corresponding to $${\mathrm{(H}}_k^t{\mathrm{-H}}_k^{\infty }{\mathrm{)/(H}}_k{\mathrm{-H}}_k^{\infty }\text{)≈0.1}$$ . The product H_kα₉₀ was relatively independent of time. The rate constant τ at 60°C was 885 min, independent of sulfur content. The constant terms, i.e., the initial minus the final anisotropy and dispersion (H_k − H_k^∞) and (1/α₉₀−1/α₉₀^∞) were functions of the sulfur content. ``Stabilization'' reduced H_k − H_k^∞ by a factor of about 5 without affecting the rate constant. The change in kinetics with sulfur content is attributed to the changes in isotropic stress, defects and impurities in the film. The higher impurity concentrations are believed to influence a larger fraction of the atom pairs, promoting their reorientation in the transverse annealing field by a lower‐energy process.