Developments in bonded rare earth permanent magnets

The various factors affecting the thermal stability of rare earth bonded magnets are re-examined by analysing the behaviour of second quadrant demagnetisation curves. It is shown that oxygen adsorbed onto the alloy particle surface is the principal cause of the gradual diminution of the magnetic properties although the choice of bonding medium can be important. Precipitation hardened alloys are shown to exhibit enhanced thermal stability over the 1:5 types. In view of these results recent improvements in the stability of production material are noted. (Author)