High magneto-mechanical hysteresis-type damping in FeGaMo alloys

Optimization of the damping capacity of conventional FeCr-based ferromagnetic high damping alloys (HDAs) usually involves a trade-off in terms of degradation of mechanical properties due to grain coarsening caused by high-temperature annealing. In this work, new ferromagnetic HDAs of FeGaMo alloys with different Mo contents are reported, which can exhibit high damping when treated in a medium temperature range. Among these alloys, the alloy with Mo content of 2 at% exhibits the best damping capacity of 4.20 × 10−2 (Q−1, equivalent to a special damping capacity SDC of 0.26). It is found that the Mo element has a high solid solubility in the FeGa alloy, and when the Mo content is 2 at%, only isolated tiny precipitations are observed in the matrix. These small precipitates have a negligible effect on hindering domain motion, and the corresponding coercivity change is extremely weak compared to the Mo-free FeGa alloy. As the Mo content increases to 4 at% or 6 at%, Mo-rich phases precipitate within the grains and along the grain boundaries, resulting in an increasing coercivity. Interestingly, as the Mo content increases, the domain density in the (001) and (110) surfaces gradually increases and the arrangement of magnetic domains becomes more tortuous due to the decrease in the magnetocrystalline anisotropy constant. For the FeGaMo alloy with 2 at% Mo content, the high damping capacity mainly arises from the energy loss caused by the high density of irreversible motion of domain walls (DWs) under the applied stress, and as the Mo content continues to increase, the significant precipitation of Mo-rich phases severely restricts the movement distance of DWs, leading to a decrease in damping. This work provides valuable insights for the design and research of new ferromagnetic high damping materials in the future.