The effect of 20 kinds of additional elements have been studied to increase the intrinsic coercivity for Co substituted Nd-Fe-B sintered magnets. The addition of Ga was found to increase iHc more than any other elements.
The effects of Ga addition on magnetic properties and thermal stability were investigated for Nd (Fe0.72Co0.2B0.08)5.6 and Nd0.8Dy0.2 (Fe0.86Co0.06B0.08)0.5 magnets. A combination of both Ga and Nb or Ga and W additions improved thermal stability which was attributed to the increase of iHc and good squareness by finer grains.
Typical Ga added 2 sintered magnets and their magnetic properties and exposure temperatures to keep the irreversible losses under 5% (Pc=2) were as follows.
[1] Nd(Fe0.7Co0.2B0.08Ga0.02)5.6: Br=12.2 KG, iHc=16.5 KOe and (BH)max=35.2 MGOe/140°C
[2] Nd0.8Dy0.2(Fe0.835CO0.06B0.08Nb0.015Ga0.01)5.5: Br=10.45 KG, iHc=27.1 KOe and (BH)max=26.2 MGOe/260°C