Permeability, magnetomechanical coupling and magnetostriction in grain-oriented rare earth–iron alloys

Abstract

Grain-oriented samples of highly magnetostrictive rare earth–iron compounds have been prepared. These samples possess lower inhomogeneous strains than found in the random polycrystalline RFe2 compounds, resulting in much higher values of relative permeability (μr) and magnetomechanical coupling (k33). A partially oriented Th.20Dy.22Ho.58Fe1.95 sample was prepared using a pyrolytic Bridgman type boron nitride crucible. At a bias field of 100 Oe k33=.73, which is considerably larger than found in the random polycrystal of the same composition. A relative permeability of 36 occurs in this same sample when a low ac drive of 1.6 Oe rms is used. A second fabrication method using a horizontal zone technique with a supporting ’’cold finger’’ was employed to grow the ternary Tb.27 Dy.73Fe1.98. The low ac drive values of k33 and μr were .74 and 19 respectively. The permeability at low bias was found to possess a sharp ac drive dependence. Near zero bias, when the drive was changed from 1.6 Oe rms to 13 Oe rms, μr in the quaternary increased from 36 to 98. In the ternary the values of μr near zero bias increased from 19 to 61. Magnetostriction measurements on both samples show a significant increase in dλ/dH and λs over the random polycrystals.