RARE-EARTH MAGNETS FOR APPLICATIONS OVER A WIDE TEMPERATURE-RANGE

Sm2Co17-type sintered magnets and Nd-Fe-B die-upset magnets have been investigated over the temperature range 4.2-423 K Their magnetic prope rties were compared with those of SmCo5 and Nd-Fe-B sintered magnets. This study indicates that the Sm2Co17-type magnets appear to be the be st for applications at high temperatures up to 423 K. The magnetic pro perties of a Sm2Co17 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 Sm2Co17 m agnet 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 stab ility compared to their die-upset counterparts. The second quadrant lo op of the Nd-Fe-B magnets exhibit an anomalous behavior at 4.2 K due t o the spin reorientation phenomenon which occurs at 140 K.