Nanoheterogeneity response in large-magnetostriction Fe-Ga alloys: An in-situ magnetic small-angle neutron scattering study

The underlying mechanism of large magnetostriction in Fe-Ga alloys is obviously beyond the conventional domain rotation and twin boundary motion, but has been attributed to the nanoscale magnetic heterogeneities. However, the nanoheterogeneity response as well as the interaction with matrix during magnetization process is still an open question. Through in-situ magnetic small-angle neutron scattering (SANS) study on a Fe ₈₁Ga ₁₉ alloy, the present work clearly reveals that the reorientation of nanodomains relevant to face-centered-tetragonal L6 ₀ nanoprecipitates occurs at relatively lower fields than that of the magnetic domains. These nanoheterogeneities show a larger magnetic correlation length than their size, ensuring the exchange coupling between nanoprecipitates and matrix as well as the flipping of their magnetizations. This process contributes to the low-field-triggered large magnetostriction, unlike that induced by non-180° domain switches in the homogeneous magnetostrictive materials (such as Terfenol-D). Further study reveals that the correlation length can be effectively tuned by simple heat-treatment, which in turn significantly enhances the magnetostriction without enlarging the triggering field. Consequently, this work contributes to uncover the physical mechanism of the large heterogeneous magnetostriction besides the typical magnetic domain theory, and may also provide a general guideline for achieving tunable magnetostriction in heterogeneous ferromagnets.