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 (μ_r) and magnetomechanical coupling (k₃₃). A partially oriented Th_.20Dy_.22Ho_.58Fe_1.95 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_.73Fe_1.98. The low ac drive values of k₃₃ and μ_r 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, μ_r in the quaternary increased from 36 to 98. In the ternary the values of μ_r near zero bias increased from 19 to 61. Magnetostriction measurements on both samples show a significant increase in dλ/dH and λ_s over the random polycrystals.