THE STRESS DEPENDENCE OF K33, D33, LAMBDA AND MU IN TB0.3DY0.7FE1.95

DC field measurements of lambda, d33, k33 and mu under uniaxial prestresses up to approximately 20 MPa have made on a 152mm long 6mm diameter grain oriented rod of Tb0.3Dy0.7Fe1.95 prepared by a free float zone technique. The lambda vs H curve shows a negative dip at low fields which persist to approximately 20 MPa. The maximum negative strains approximately -120ppm occur under approximately 2 MPa which is also the pressure at which optimum permeability and magnetomechanical coupling occur. The origin of the negative strains is discussed in the light of earlier predictions based on an anisotropic rotational model for magnetisation and magnetostriction and the practical consequences are discussed.