Structural and soft magnetic properties of Fe73.5Nb3M1Si13.5B9 (M=Cu, Mn, Pt)

Abstract

The magnetic and the structural properties have been investigated for Fe73.5Nb3M1Si13.5B9 (M=Cu, Mn, Pt) alloys in their as-received and heat-treated state. Differential scanning calorimeter and scanning electrical resistivity were used to study crystallization behaviour and to examine the influence of the nucleation elements Cu, Mn and Pt on the structural and magnetic properties of Fe-based nanocrystalline materials. The temperature coefficient of resistivity above Curie temperature was found to be very low (0.2×10−4 K−1) in the Cu containing alloy as compared to the alloys which contained Mn or Pt. A broad exothermic DSC peak for the formation of Fe3Si nanoparticles was absent when Cu was replaced by Mn or Pt. Instead, a sharp exothermic peak for the formation of Fe3(SiB) phase was observed with an onset at 875 K. The magnetic properties of the three alloys measured after stress relaxed annealing were similar. However, after first-stage crystallization, the soft magnetic properties were further enhanced only in Cu containing alloys due to the formation of Fe3Si nanoparticles. Such nanoparticles together with different intermetallic phases like FeMn3 or FePt3 were formed in Mn or Pt containing alloys. Moreover, the NbFeSi phase was also formed in the latter alloys after higher temperature annealing which reduced not only the amount of the Fe3Si phase but also the grain refining effect due to the lesser amount of Nb available at the grain boundary. When Cu was replaced by Mn or Pt, the formation of different intermetallics reduced the volume fraction of Fe3Si nanoparticles and the lesser amount of grain refining Nb made the materials magnetically inferior after annealing above 775 K.