Local inhomogeneous structural origin of giant magnetostriction in Fe-Ga alloys

Melt-spun ribbons and single crystal plates of Fe₈₃Ga₁₇ alloys were studied at both nano-scale and atomic-scale to investigate the structure origin of their giant magnetostriction. The presence of nano-precipitates in the melt-spun ribbons was verified using synchrotron x-ray diffraction and was validated by small angle scattering experiment. The nano-precipitates were found to be inhomogeneously distributed within the ribbons, as peak splitting clearly observed in the diffraction patterns disappeared into broad peaks when the synchrotron beam was focused onto different parts of the same sample. Further analysis using x-ray diffuse scattering and extended x-ray absorption fine structure indicates the existence of short-range ordering (SRO) Ga-Ga pairs along the (001) direction in both the ribbon and single-crystal alloys. All experimental evidence suggests that this modified D0₃-type SRO leads to both a short-range lattice strain and a long-range symmetry breaking tetragonal distortion of the A₂ lattice. This gives rise to giant magnetostriction in the Fe-Ga alloys. In the melt-spun ribbons, the Ga-Ga pairs can aggregate into nano-sized precipitates under fast cooling and enhance the magnetostriction further.