Rare earth magnets for applications over a wide temperature range

Abstract Sm 2 Co 17 -type sintered magnets and Nd-Fe-B die-upset magnets have been investigated over the temperature range 4.2–423 K. Their magnetic properties were compared with those of SmCo 5 and Nd-Fe-B sintered magnets. This study indicates that the Sm 2 Co 17 -type magnets appear to be the best for applications at high temperatures up to 423 K. The magnetic properties of a Sm 2 Co 17 magnet at 423 K are: B r = 10.8 kG , i H c = 15.7 kOe and (BH) max = 27.1 MGOe. The irreversible loss of the Sm 2 Co 17 magnet at a permeance coefficient of 2 is 1.1% after exposure at 573 K for half an hour. Sintered Nd-Fe-B magnets exhibit better thermal stability compared to their die-upset conterparts. The second quadrant loop of the Nd-Fe-B magnets exhibit an anomalies behavior at 4.2 K due to the spin reorientation phenomenon which occurs at 140 K.