Electromechanical coupling coefficient (K₃₃) of Tb-Dy-Fe giant magnetostrictive alloy

The nominal Tb_0.3Dy_0.7Fe_1.90 magnetostrictive material oriented along <110> and <112> have been prepared by zone melting unidirectional solidification. Vacuum annealing at 900°C for 4 or 48 h has been carried out. The electromechanical coupling coefficient (K₃₃) is determined by the impedance resonance frequency tested by using AC impedance instrument. K₃₃ of the samples oriented along <110> and <112> increases comparatively to the as-cast samples. With the increase of DC magnetic field, K₃₃ increased initially, and then decreased. With the increase of stress from 0 MPa to 10 MPa, K₃₃ increased, but at 15 MPa K₃₃ is reduced. K₃₃ is sharply improved after proper heat treatment, which can be attributed to the change of the magnetic domain configuration after heat treatment.