Anomalous large circular susceptibility in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 wires

Abstract The circular susceptibility χ of amorphous and nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 wires was measured under an axially applied field H up to 89 kA/m. The χ ( H ) of the amorphous sample may be well described by the core–shell model of positive magnetostrictive amorphous wires; however, after nanocrystallization, the χ ( H ) can be a few to few tens times greater than the ideal circular susceptibility χ id = M s / H deduced from the assumption of a zero anisotropy. This phenomenon is discussed in terms of a negative local anisotropy field H k ∗ resulting from the existence of magnetic inclusions, but its actual mechanism has to be further studied.