It was shown [1] that soft magnetic properties of the Fe_86-xNb_xB₁₄ (x=2-8) amorphous alloys can be improve by 1 h annealing at temperatures close to the crystallization temperature. Such an optimization annealing causes an increase of initial magnetic permeability μ (for the best alloy x=6, μ=3x 10⁴), and a reduction of coercive field (1-3 A/m). The observed effect was attributed to annealing out of free volume leading to formation of small iron clusters. An unfavorable effect of the high Nb content is a relatively low Curie temperature (390 K) which can be improved by a partial replacing of Fe by Co.

The aim of the paper is to study magnetic properties, crystallization and the optimization effect of the Fe₇₂Co₁₀Nb₆B₁₂ amorphous alloy for which the Curie temperature was determined as 515 K. Magnetic properties were studied by making use of: permeability measurements (Maxwell-Wien bridge, f=1 kHz, H=0.5 A/m), magnetic after-effect Δμ/μ (Δμ=μ(t₁=30s)-μ(t₂=1800s), t₁, t₂ times after demagnetization), coercive field H_c (permalloy probe) and magnetization curves (fluxmeter).

It was shown that soft magnetic properties can be optimized by 1 h annealing at 675 K. For optimized samples μ=10⁴ and H_c=15 A/m. The crystallization was examined by applying measurements of magnetization (magnetic balance) with heating rates 3-10 K/min and derivation scanning calorymetry (5-20 K/min). The activation enthalpy of the nanocrystallization was determined as 3.8 eV.

[1] G.Haneczok, A.Chrobak, P.Kwapuliński, Z.Stokłosa, J.Rasek, N.Wójcik, Proceedings of International Conference on Soft Magnetic Materials, SMM'16, Düsseldorf September 2003, Verlag Stahleisen GmbH 2004, p.603.

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