MAGNETOMECHANICAL DAMPING IN FESIB AMORPHOUS WIRES

Magnetomechanical damping of amorphous wires has been measured as a function of the surface torsional strain (frequency approximately 1-4 Hz) at different applied tensile stresses and applied magnetic fields. The wire used in these measurements has a composition of Fe77.5B15Si7.5 with a diameter of 125 mum. The variation of magnetomechanical damping as a function of torsional strain shows a maximum as previously observed in ferromagnetic materials. It has been found that the main mechanism responsible for magnetomechanical damping is magnetomechanical hysteresis associated with irreversible motion of 90-degrees domain walls. The influence of macroeddy and microeddy currents is negligible at the very low frequency of measurement. The large casting stress of > 200 MPa was reduced by furnace annealing at zero field to about 2 MPa. Further annealing induced a small amount of surface crystallization. The effects of annealing, magnetic field and tensile stress on the magnetomechanical properties of amorphous wires are discussed in the light of existing models. It is shown that a model based on the distribution of intemal stress alone is unable to explain all the features of the results. A model incorporating the distribution of domain wall energy is successful in explaining the results if a correction is made for the significant strain dependence of shear modulus.