High permeability nano-crystalline FeSiBTaAg ribbons obtained by direct casting

Nano-crystalline soft magnetic ribbons, being extensively used as magnetic cores for switching power supplies, have been invariantly obtained by melt-spinning followed by post-annealing. Reported herewith are the attainment, by direct-casting without annealing, of nano-crystalline Fe77.4−xSi15.5B7TaxAg0.1 (x = 1, 2) ribbons with superior soft magnetic properties (named TAGMET after the addition of Ta and Ag). The grain size of nano-crystalline α-FeSi, from 20 to 30 nm, varies with composition and quenching speeds. As-spun Fe75.4Si15.5B7Ta2Ag0.1 ribbons consisting of ∼25 nm nano-crystals exhibit a saturation magnetization of 157 emu/g (1.45 T), an effective permeability of 56,000 at 1 kHz, and coercivity, 8 A/m. With the combination of easier manufacturing process and excellent soft magnetic properties, this alloy is competitive in industrial applications versus the well-known FINEMET.