MICROSTRUCTURES OF FE73.5SI13.5B9NB3CU1 NANOCRYSTALLINE SOFT MAGNETIC MATERIAL INVESTIGATED BY APFIM AND HRTEM

The microstructure of the Fe73.5Si13.5B9Nb3Cu1 soft magnetic material with a nanocrystalline structure has been investigated by atom probe field ion microscopy and high resolution electron microscopy. In the as-quenched amorphous sample, all the alloying elements were found to distribute homogeneously as an amorphous solid solution. In the annealed sample with the optimum soft magnetic properties, we found that two phases were present. One was bcc Fe-Si solid solution and the other was the B and Nb enriched amorphous phase with little Si content. Although some uncertainty remains regarding the distribution of Cu, the present result is consistent with earlier speculations that the bcc phase would be the Fe-Si solid solution based on the lattice parameter measurement and the Curie temperature measurement.