Excellent high-temperature magnetic softness in a wide temperature for FeCo-based nanocrystalline alloy

Abstract Structure and initial permeability (μi) of as-quenched and annealed (Fe1 − xCox)72.7Al0.8Si17.5B5Cu1Nb3 (x = 0,0.5) alloys were investigated. Substituting 50 at.% Co for Fe enhances both the Curie temperature of amorphous alloy, TcA, from 325 to 375 °C and the secondary crystallization temperature Tx2, for delaying the formation of Fe–B hard magnetic phase from 720 °C to 729 °C. The correlation between initial permeability and temperature (μi–T curve) for (Fe0.5Co0.5)72.7Al0.8Si17.5B5Cu1Nb3 alloys heating–cooling cycled at 510–640 °C was mainly analyzed. The optimum high temperature magnetic softness was found in 550 °C-annealed sample, the μi can maintain above 1400 and shows roughly a horizontal linear correlation with T from room temperature up to 600 °C, which make this alloy attractive as an affordable high-temperature soft magnetic material.