Irradiation of Iron and 5–79 Mo Permalloy with 2-MeV Electrons

Abstract

Large changes in the structure‐sensitive magnetic properties of bulk polycrystalline 5–79 Mo Permalloy resulted from irradiation with 2‐MeV electrons at ∼10¹⁷ electrons/cm² at temperatures ranging from 60° to 170°C. These changes showed an approximately linear dependence on sample thickness from 0.10 to 0.25 mm. In addition, extreme rectangularities in the magnetization curves and hysteresis loops were obtained. For example, the maximum slope of the magnetization curve for a 0.10‐mm sample increased from ΔB/ΔH=0.3×10⁶ to ΔB/ΔH=4.3×10⁶. This unusual steepness is evidence of the effectiveness of electron irradiation in influencing order in 5–79 Mo Permalloy at temperatures well below the ordering temperature, and without an applied magnetic field. Iron, irradiated under the same conditions, showed no changes in its magnetic properties. The range of 2‐MeV electrons in these materials is ∼1.3 mm, well beyond the maximum sample thickness used. The calculated fractional number of atoms displaced is ∼5.3×10⁻⁶, which decreases slightly with thickness, unless one considers the difference between the actual path length of the electron in the sample (due to multiple scattering) and the actual sample thickness. If this difference between the average path length and sample thickness is calculated according to the theory of Yang, then the fractional number of atoms displaced increases linearly with sample thickness, in agreement with the thickness dependence of the radiation induced magnetic properties changes observed.