Structure and magnetic properties of amorphous and nanocrystalline Fe 40Co 40Cu 0.5Zr 9Al 2Si 4B 4.5 alloys

Crystallisation behaviour and magnetic properties of as-spun and annealed Fe ₄₀Co ₄₀Cu _0.5Zr ₉Al ₂Si ₄B _4.5 alloy have been studied. The annealing was performed at 873 K for 15 min. XRD and TEM studies shows the formation of nanocrystalline α-(Fe,Co)(SiAl) particles with 7.5±2 nm in diameter dispersed in an amorphous matrix. The Curie temperature of the as-spun amorphous ribbon is 736 K. Saturation magnetisation of the annealed sample decreases at a rate of 0.5 emu/g/K in the measured temperature range of 300-1000 K. Excellent room temperature AC magnetic properties are achieved for the nanocrystalline sample. The low value of the imaginary part of the permeability and the high cut-off frequency (20 kHz) suggest that the eddy current contribution in the annealed materials is low. The coercivity of the annealed sample remains almost constant at 95 A/m up to the frequency of 20 kHz. High saturation magnetisation, high Curie temperature and excellent soft magnetic properties in the nanocrystalline state suggests that Fe ₄₀Co ₄₀Cu _0.5Zr ₉Al ₂Si ₄B _4.5 alloy is a strong candidate for high temperature magnetic application.