The influence of composition and field annealing on magnetic properties of FeCo-based amorphous and nanocrystalline alloys

Abstract

We report the influence of composition and very high transverse field annealing on the magnetic properties and structure of four FeCo-based amorphous and nanocrystalline alloys. The compositions (Fe 50Co 50) 89Zr 7B 4 and (Fe 65Co 35) 89Zr 7B 4 were investigated changing the Fe:Co ratio from 50:50 to 65:35. (Fe 50Co 50) 85Zr 2Nb 4B 8.5 was chosen to investigate Nb substitution for Zr in an FeCo-based alloy. This substitution is shown to increase the magnetostrictive constant, λ S , of the nanocrystalline alloy from 36×10 −6 to 54×10 −6. The composition (Fe 65Co 35) 84Cr 5Zr 7B 4 was studied to investigate the influence of Cr on intergranular coupling across the amorphous matrix. Samples of each composition were annealed in the amorphous state at 300 °C and in the nanocrystalline state at 600 °C. Field annealing was performed in 17 T transverse field in an inert atmosphere. Frequency-dependent magnetic properties were measured with an automatic recording hysteresisgraph. Static magnetic properties were measured with a vibrating sample magnetometer. The mass-specific power loss of the alloys decreased with field annealing in both the nanocrystalline and amorphous states for some frequency and induction combinations. Furthermore, the hysteresis loops are sheared after field annealing, indicating a transverse magnetic anisotropy. The nanocrystalline (Fe 50Co 50) 85Zr 2Nb 4B 8.5 composition has a lower relative permeability than the other compositions.