Induced Magnetic Anisotropy Created by Magnetic and Stress Annealing of Iron-Aluminium Alloys

Abstract

Polycrystalline samples of five iron-aluminium solid solutions were subjected to various heat treatments either (i) in a strong magnetic field, or (ii) under tensile stress. For treatment (i) the samples were in the form of cylinders, while in case (ii) they were machined into this form after stress treatment. Torqueazimuth plots were obtained from each sample by means of a torque magnetometer; further heat treatments were then applied, followed again by torque measurements, to permit correction for the intrinsic anisotropy resulting from unavoidable preferred orientation of grains. The maximum value of anisotropy, whether field- or stress-induced, arises at 21-22 at.% aluminium. Induced anisotropy energies of up to 17 000 erg cm^-3 were recorded. A variety of heat treatments were used to explore the inhibiting effect of spontaneous long- or short-range order on the development of induced anisotropy. This inhibiting effect is pronounced, and in stoichiometric Fe₃Al it is possible to prevent almost completely the creation of induced anisotropy. Such inhibition is to be expected if the induced anisotropy is caused by directional order. A close correspondence is observed between the composition dependence of induced anisotropy and that of the Zener internal friction.