Magnetic Structural Analysis of Nanocrystalline Soft Magnets by Small-Angle Neutron Scattering

Nanocrystalline soft magnets have attracted significant attention for their improvement of energy conversion devices. It has been considered that the partial nanocrystallization of amorphous structures is a key to macroscopic magnetic softness. However, the mechanism has not been clarified because of inadequate knowledge of the magnetic nanostructures connecting microscopic crystalline structures and macroscopic magnetic properties. Here, we performed small-angle neutron scattering (SANS) for Fe
₈₅
Si
₂
B
₈
P
₄
Cu
₁
alloy ribbons (NANOMETs). Rapidly quenched ribbons were annealed at 375 °C and 400 °C for 5 min. The X-ray diffraction pattern for the as-quenched ribbons did not exhibit peaks. Therefore, their atomic structure can be considered amorphous. Oppositely, evident α-iron peaks were observed for the ribbons annealed at 375 °C and 400 °C. The nuclear scattering contribution in SANS indicates that the precipitations were formed with sizes in the nanoscale. The magnetic scattering contribution in SANS for the as-quenched ribbon, whose intensity decreased with an increase in the scattering vector
q
in proportion to
q
⁻⁴
, disappeared when magnetic fields were applied. This behavior is consistent with the conventional magnetic domain picture. Oppositely, the reduction rates of the magnetic scattering contribution for
q
were nonmonotonous for the nanocrystallized ribbons. Furthermore, strong magnetic scattering was observed in the directions inclined to the magnetic field. This feature is similar to that reported for Fe–(Nb, Zr)–B alloy ribbons (NANOPERMs). The knowledge on the magnetic nanostructures characterized by the unusual angular dependence of magnetic scattering would be helpful to considering the relationship between partially nanocrystallized structure and macroscopic soft magnetic properties.