Structure and Properties of R – (Fe, Co) – B (R = Nd, Dy, Ho) Permanent Magnets with Low Temperature Coefficient of Induction

Resumo

Two groups of sintered permanent magnets with reduced temperature coefficient of induction (TCI) are considered, i.e., (A ) (Nd_0.64Dy_0.36)₁₆(Fe_{1 – x}Co_x)_77.5Cu_0.1Ga_0.3B_6.1(x = 0.22 – 0.36) and (B) Nd_{0.64 – z}Dy_0.36Ho_z)₁₆(Fe_0.64Co_0.36)_77.5Cu_0.1Ga_0.3B_6.1 ( z = 0.08 – 0.26). It is shown that substitution of 36% Fe by Co raises the Curie temperature of the magnets to 576°C and lowers the TCI to ∣ − 0.02 ∣  % /K in the range of 27 – 120°C. Substitution of Nd by Ho lowers the TCI additionally to zero at z = 0.17 and changes it to ∣ + 0.009 ∣  % /K at z = 0.26. The results of the study of the phase composition and of the microstructure of the magnets make it possible to explain the observed lowering of the coercivity under the alloying.