Bremsstrahlung radiation effects in rare earth permanent magnets

Advances in rare earth permanent magnet (REPM) technology have made possible new applications. Two such applications are the use of permanent magnetic lenses for accelerator and beam transport systems and the expanding use in undulators and wigglers of synchrotron radiation and free electron laser systems. Both applications involve potential exposure of REPM's to high radiation fields. We have investigated the radiation hardness of several different varieties of REPM's up to 2 gigarads of absorbed dose from a mixed electron-photon (bremsstrahlung) field. Sm2Co17, Nd2Fe14B and an experimental REPM, Pr15Fe79B6, from several different manufacturers have been investigated. Of the samples irradiated, Sm2Co17 proved to be the most resistant to bremsstrahlung radiation. However, details of manufacturing techniques produced significantly different results. We observed that REPM's of nominally identical stoichiometric composition from different manufacturers did not show the same rate of remanence loss. We present details of our experiment and absorbed dose modeling and a summary of radiation effects measurements of which we are aware. Our study of these radiation damage experiments lead us to the empirical observation that the order of radiation hardness is Sm2Co17, SmCo5 and Nd2Fe14B, regardless of the source of radiation, i.e., gammas, electrons, protons or neutrons.