Magnetic properties and microstructure in NdFeB strip-cast permanent magnets

Abstract Nd8Fe73Co5Hf2B12 alloys were cast as strips (continuous ribbons with thickness t=100–160 μm ) by a chill-disk melt spinning technique (v disk =3 m / s ) from a master alloy prepared by arc-melting (A) and from two previously prepared alloy components (B). Samples obtained by the B procedure had, in the as-cast state, magnetic properties with a coercivity, i H c =813 kA / m (not saturated at 1.6 T applied field), remanence, μ 0 M r =0.5 T , and maximum energy product, (BH max =107 kJ / m 3 ) . By comparison, the magnetic properties of A type samples obtained by annealing 5 min at 700°C are i H c =513 kA / m , μ 0 M r =0.52 T , (BH max =63 kJ / m 3 ) . Based on δM and irreversible susceptibility plots we suggest a smaller exchange coupling of the grains in sample A as compared to sample B.