Domain Orientation in Mo Permalloy and 65 Ni–Fe by Electron Irradiation at 100°C

Abstract

A variety of effects have been observed in flat‐ring polycrystalline samples of 5–80 Mo Permalloy and 65 Ni–Fe irradiated by 2‐MeV electrons at temperatures within the range of 70° to 170°C. For the Mo Permalloy samples, application of a 0.22‐Oe field during irradiation to 1.10×10¹⁷ e/cm² resulted in square hysteresis loops with B_r as high as 6700 G (possibly a record high) but with little or no increase in H_c. In zero applied field, H_c increased and B_r and μ_m decreased in all cases, but loop shapes were either rectangular, constricted, tristable, or conventional. The tristable loops, which appeared after a run in which the beam was interrupted several times, resemble those theorized by Kaya for the case of a material having two dominant anisotropy axes. Irradiation of 65 Ni–Fe with a 1‐Oe field and a dose of 7×10¹⁷ e/cm² resulted in increases of ∼100% in B_r and μ_m but accompanied by a 50% increase of H_c. The ``directional order theory'' for magnetic annealing (including the case of zero applied field) can be applied to the above results. However, at any given temperature the vacancy concentration increase due to irradiation accelerates the ordering process through enhancement of the diffusion rate. Hence directional ordering can occur at relatively low temperatures in irradiated materials. The thresholds of damage (in zero field) for 5–80 Mo Permalloy and 65 Ni–Fe were >0.17×10¹⁷ and >1.0×10¹⁷ e/cm², respectively. Post‐irradiation measurements indicate long‐term stability of all of the above effects.