Some nanocrystalline Fe-based soft magnetic alloys have recently been found that exhibit high flux density (Bs) combined with good soft magnetic properties. Among these alloys, the highest Bs with high permeability (μe) has been achieved for the Fe-Zr-B ternary alloys, because an amorphous phase with Fe concentrations higher than these of the other nanocrystalline alloys is obtained owing to the high glass-forming ability of Zr and the formation of a nanocrystalline bcc phase without additional nonmagnetic elements of Cu, Nb, or Ge. For example, the Bs and μe (1 kHz) are 1.7 T and 14000, respectively, for Fe91Zr7B2. Furthermore, we have found that a similar nanocrystalline bcc structure is obtained in Fe-M-B (M = Hf, Nb) alloys and these alloys exhibit nearly the same magnetic properties as the Fe-Zr-B alloys. The changes in Bs and μe as a function of annealing temperature for Fe90Zr7B3, Fe89Hf7B4 and Fe84Nb7B9 alloys are very similar because there is no difference in the crystallization behavior of the three alloys. The highest values of μe at 1 kHz and Bs attained 22000 and 1.63 T for Fe90Zr7B3, 32000 and 1.59 T for Fe89Hf7B4, and 22000 and 1.49 T for Fe84Nb7B9. The core losses at 50 Hz, 0.2-1.4 T and the frequency range 10-300 kHz for these alloys are considerably lower than those for Fe-based amorphous and Fe-3%Si alloys now in use as core materials in various transformers.
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