Alloying effect on the magnetic properties of RFeB-type bulk magnets

Abstract

Composition dependence on the magnetic properties of directly casted cylindrical R FeB M -type magnets with diameters from 0.7 mm to 1.5 mm has been studied. In order to refine the microstructure for improving the magnetic properties of bulk magnets with various sizes, the following ways were adopted in the alloys: (1) changing the boron concentration, (2) substituting different kinds of refractory elements for Fe, (3) adding a slight carbon and finally, (4) adopting multi-component refractory elements. The experimental results showed that the Nd 9.5 Fe 72.5 Ti 3 B 15 bulk magnets with a diameter of 0.7 mm demonstrated the optimal magnetic properties of B r = 6.5 kG, i H c = 10.3 kOe and ( BH ) max = 8.7 MG Oe, while the highest i H c of 16.2 kOe was achieved for the Pr 9.5 Fe 71.5 Nb 4 B 15 magnet. Meanwhile, the diameter of the magnets could be increased to 0.9 mm preserving the attractive magnetic properties by the substitution of 0.5 at% Zr for Ti in the Nd 9.5 Fe 72.5 Ti 3 B 15 magnet. Finally, the directly casted Nd 9.5 Fe 72.5− y Ti 2.5 Zr 0.5 Cr y B 15− x C x ( x = 0.25–1; y = 0–3) magnets with a larger diameter of 1.3 mm exhibited attractive magnetic properties of B r = 5.3–6.1 kG, i H c = 7.2–12.5 kOe and ( BH ) max = 6.5–7.2 MG Oe.