Proceedings of Space Nuclear Conference 2007 Boston, Massachusetts, June 24-28 2007 Paper 2036 THERMAL STABILITY AND RADIATION RESISTANCE OF SM-CO BASED PERMANENT MAGNETS Jinfang Liu, Payal Vora, Peter Dent and Michael Walmer Electron Energy Corporation 924 Links Ave, Landisville, PA 17538, USA Tel: 717-898-2294, Fax: 717-898-0660, Email: jfl@electronenergy.com Christina Chen University of Dayton Research Institute KL501, 300 College Park Ave, Dayton, OH 45469,USA Joseph Talnagi Ohio State University Research Reactor 1298 Kinnear Road, Columbus, OH 43212, USA Suxing Wu and Martin Harmer Center for Advanced Materials and Nanotechnology, Lehigh University 5 East Packer Avenue, Bethlehem, PA 18015, USA Abstract – We will review in this paper the recent data on thermal stability and radiation resistance of rare earth permanent magnets. Scanning electron microscopy analysis suggests that the affected surface layer of SmCo magnets is almost undetectable (less than 1 micron) after exposure to a temperature lower than 550 o C for 240 hours under vacuum. For SmCo T550 magnet samples with 10mm in diameter and 10mm long, magnetic properties do not change much up to its maximum operating temperature. SmCo based magnets have better neutron radiation resistance as compared to Nd-Fe-B type magnets. It is noted that the radiation resistance and thermal stability are somewhat related because the irradiation damage is most likely caused by a radiation-induced thermal spike. Sm(Co,Fe,Cu,Zr) z magnets do not show any noticeable changes in magnetic properties while Nd 13 Dy 2 Fe 77 B 8 samples lost almost 100% of its magnetic flux with a neutron flux of 10 16 n/cm 2 . It is also worthwhile to point out that the magnetic properties of irradiated Nd-Fe-B type magnets are recoverable after re-magnetization, which indicates that radiation damage is caused by a thermal spike instead of microstructure changes. I. INTRODUCTION Sintered SmCo 5 , Sm 2 TM 17 and Nd 2 TM 14 B magnets were developed in 1960s, 1970s and 1980s, respectively (TM: Transition Metals) 1-3 . SmCo 5 and Sm 2 TM 17 magnets have good thermal stability and radiation resistance while Nd 2 TM 14 B magnets exhibit higher room-temperature magnetic properties. Rare earth permanent magnets have found applications in a variety of industries due to their superior magnetic properties. NASA applications include high power ion propulsion engines and alternators in high efficiency dynamic power converters. In the high power ion engines, the electrons collide with Xe atoms, ionizing them. Permanent magnets create an axial magnetic field that extends the electron paths and increases the probability of an ionizing collision. Having a consistent magnetic field is essential for ion engine performance. These high power ion engines would operate at elevated temperatures under vacuum and radiation. In space, existent radiation comes from the trapped particles (electrons and ions) in the radiation (Van Allen) belts, solar flare protons and galactic cosmic rays. Figure 1 shows Xenon ion propulsion engine with high temperature magnet used in Deep Space I. 4