EFFECTS OF NANOCRYSTALLIZATION UPON THE SOFT-MAGNETIC PROPERTIES OF CO-BASED AMORPHOUS-ALLOYS

Amorphous samples of Vitrovac(R) 6025 metallic alloys were nanocrystal lized by thermal annealing at temperatures in the range 576-716 K, wel l below the crystallization temperature (831 K, as obtained by differe ntial scanning calorimetry at 20 K/min) and times in the range 10-90 m in. Initial magnetic permeability exhibited a maximum of - 109 000 (fr om approximately 20 000 for the as-quenched state) for annealing times of approximately 15 min, and then a decrease toward a plateau value ( 30 000-40 000) for longer times. Domain wall relaxation frequency show ed the opposite behavior, a minimum of approximately 9 kHz (from 40 kH z for the as-quenched value) for the permeability maximum, and then a stabilization at approximately 15 kHz. Transmission electron microscop y observations confirmed that for annealing times up to 60 min., cryst allite size is smaller than 30 nm. Permeability and relaxation frequen cy results are interpreted in terms of the dependence of wall bulging on anisotropy and free-wall surface area between pinning sites.