Radiation-Induced Changes in Magnetic Properties of Nd-Fe-B Permanent Magnets

摘要

The high remanence and intrinsic coercivity of Nd-Fe-B magnets make them desirable for use in the accelerators. Use in the radiation environment of an accelerator requires that the sensitivity of these magnets to radiation be determined and the mechanisms responsible be understood. We present results comparing the relative radiation sensitivity of a number of commercially available Nd-Fe-B magnets. Small samples of these magnets were irradiated at the Omega West Reactor in a neutron flux of 2 x 10 sup 13 n/cm sup 2 s at a temperature of 350 deg K (77 deg C). At various time intervals during the irradiation, samples were removed from the reactor and the open-circuit remanence measured. We also measured the second quadrant demagnetization curve of samples before and after neutron irradiation to monitor changes in remanence and intrinsic coercivity. Our results show that the sensitivity to radiation varies widely among magnets from different vendors. In general, these samples showed a decrease in the remanence and an increase in the intrinsic coercivity. We present results showing that the rate of remanence decay decreases monotonically with increasing length-to-diameter (L/D) ratio for samples of the same material. Thus, it is important to compare decay rates corrected to some constant L/D ratio. 7 refs., 3 figs., 2 tabs. (ERA citation 13:001583)