Computer Simulation of Enhancement of Coerciviy in Nd-Fe-B/(Nd,Dy)-Fe-B Composite Magnets

The coercivity $H_c$ of $Nd_2Fe₁₄B$ magnets and $Nd_2Fe₁₄B/(Nd_0.7Dy_0.3)_2Fe₁₄B$ composite magnets were calculated by computer simulation based on the micromagnetic theory under assumptions that $Nd_2Fe₁₄B$ and $(Nd_0.7Dy_0.3)_2Fe₁₄B$ grains have magnetically deteriorated layers on their surfaces and diffusion of Dy from $(Nd_0.7Dy_0.3)_2Fe₁₄B$ grains to $Nd_2Fe₁₄B$ ones through the contacting boundaries recovers the magnetic anisotropy of the deteriorated layers of $Nd_2Fe₁₄B$ grains. $H_c$ of $Nd_2Fe₁₄B/(Nd_0.7Dy_0.3)_2Fe₁₄B$ composite magnets increased by the diffusion of Dy from $(Nd_0.7Dy_0.3)_2Fe₁₄B$ grains to $Nd_2Fe₁₄B$ ones and the resultant recovery of the anisotropy field of deteriorated layers of $Nd_2Fe₁₄B$ grains. The $H_c$ vs fraction of $(Nd_0.7Dy_0.3)_2Fe₁₄B$ grains curve were convex for the magnets with the degree of alignment between 0.94 and 0.99, which suggests that the above composite magnets have larger $H_c$ values than the alloy-magnets with the same Dy content, and that we can save the consumption of Dy by using these composite magnets.