Thermal Stability and Soft Magnetic Properties of Fe–Nb–B Amorphous Alloys with High Boron Concentrations

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Abstract
Ferromagnetic amorphous Fe–Nb–B alloys containing 30 at%B were found to exhibit a large supercooled liquid region with a temperature interval over 50 K before crystallization and the largest ΔTx(=Tx−Tg) reaches 71 K for Fe62Nb8B30. The ΔTx is strongly dependent on B content, while the soft magnetic properties of saturated magnetization (Is), permeability (μe) and saturated magnetostriction (λs) are dependent on Nb content. The Fe62Nb8B30 amorphous alloy exhibits good soft magnetic properties of 0.68 T for Is, 2.6 A/m for coercive force (Hc), 19300 for μe at 1 kHz and 7.7×10−6 for λs. The crystallization takes place through a single exothermic reaction, accompanying the simultaneous precipitation of the three crystalline phases of α-Fe, Fe2B and FeNb2B2. The crystallization mode which requires long-range atomic rearrangements plays a dominant role in achieving the high stability of the supercooled liquid against crystallization.