The irreversible motion of magnetic domain walls in ferromagnets can dissipate a large portion of the elastic energy,and the associated damping capacity is proportional to the magnetostriction constant.In contrast,here we found that the damping capacity of the large magnetostriction Fe-Ga alloys can be enhanced by 2-3 times through introducing structural defects including interfacial dislocations and stacking faults,despite that these defects deteriorate the magnetostriction.These structural defects were introduced by aging the BCC(body-centered-cubic)solution-treated precursor,for which the formation of mechanically harder FCT(face-centered-tetragonal)and/or FCC(face-centered-cubic)phases can result in high-density partial dislocations at the semi-coherent phase interfaces and quasi-periodically stacked nano-layer substructure inside the FCC variants.The structural defects act as extra damping sources besides the magnetic domain walls because the structural accommodation of the semi-coherent phase interfaces between BCC and FCT/FCC nanoprecipitates with different elastic moduli and the nano-layer substructure towards long-range ordered periodical stacking can dissipate a large portion of mechanical energy.These findings suggest that introducing structural defects provides fresh freedom to design high damping ferromagnetic materials.