Magnetic properties on sintered permanent magnets R-Fe-Cu-B (R=Pr, Nd)

Radially anisotropic Pr₁₅Fe_77.5Cu_1.5 B₆ permanent magnets have been prepared from hydrogen decrepitated (HD) powders by conventional powder metallurgy processes. The best magnetic properties obtained along the radial directions are as follows: (BH)_max=10.5 MG-Oe, B_r=7.5 kG, and iH_c=8.5 kOe. Since Pr₂(Fe,Cu)₁₄BH_x exhibits planar anisotropy, the tetragonal c-axis of the HD powders should lie in the plane perpendicular to the field direction during alignment compaction. This style of radial alignment is not changed in the subsequent dehydrogenation and sintering processes. The easy direction of magnetization of the magnet can be changed by alloy design, switching from radial directions to the field direction with the addition of 33 wt.% or more of Nd-Fe-B. Further addition of Nd-Fe-B monotonically increases both B_r and (BH)_max. For the Nd-Fe-Cu-B system, a small concentration of 1.5 at.% Cu dramatically deteriorates the magnetic properties of the sintered magnet due to the extensive precipitation of free iron