NdFeB system sintered magnet
A NdFeB system sintered magnet produced by the grain boundary diffusion method that has a high coercive force and squareness ratio with only a small decrease in the maximum energy product. The NdFeB system sintered magnet has a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (the “Dy and/or Tb” is hereinafter called R H ) attached to and diffused from a surface of the base material through the grain boundary inside the base material by a grain boundary diffusion treatment, wherein the difference C s -C d3 between the R H content C s (wt %) in the grain boundary reaching the surface to which R H is attached and the R H content C d3 (wt %) in the grain boundary at a depth of 3 mm from the aforementioned attachment surface is equal to or smaller than 20 wt %.
1. A NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (R H ) attached to and diffused from a surface of the base material through a grain boundary inside the base material by a grain boundary diffusion treatment,
wherein a difference C s -C d3 between an R H content C s (wt %) in the grain boundary reaching the surface to which R H is attached and an R H content C d3 (wt %) in the grain boundary at a depth of 3 mm from the aforementioned attachment surface is equal to or smaller than 20 wt %.
2. The NdFeB system sintered magnet according to claim 1 , wherein a difference C s -C d1 between the R H content C s (wt %) in the grain boundary reaching the attachment surface and an R H content C d1 (wt %) in the grain boundary at a depth of 1 mm from the attachment surface is equal to or smaller than 15 wt %.
3. The NdFeB system sintered magnet according to claim 1 , wherein a percentage of a total volume of a carbon rich phase in a rare-earth rich phase at the grain-boundary triple points in the base material to a total volume of the rare-earth rich phase is equal to or lower than 50%.
4. The NdFeB system sintered magnet according to claim 1 , wherein a carbon content of the entire base material is equal to or lower than 1000 ppm.
5. The NdFeB system sintered magnet according to claim 1 , wherein an average grain size of main-phase grains which are grains constituting the base material is equal to or smaller than 4.5 μm.