THERMAL STABILITY AND RADIATION RESISTANCE OF SM-CO BASED PERMANENT MAGNETS

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 2Fe 77 B8 samples lost almost 100% of its magnetic flux with a neutron flux of 10 16 n/cm � . 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.