Magnetic properties and microstructure in NdFeB strip-cast permanent magnets

Nd8Fe73Co5Hf2B12 alloys were cast as strips (continuous ribbons with thickness t=100–160 μm) by a chill-disk melt spinning technique (vdisk=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, iHc=813 kA/m (not saturated at 1.6 T applied field), remanence, μ0Mr=0.5 T, and maximum energy product, (BHmax=107 kJ/m3). By comparison, the magnetic properties of A type samples obtained by annealing 5 min at 700°C are iHc=513 kA/m, μ0Mr=0.52 T, (BHmax=63 kJ/m3). Based on δM and irreversible susceptibility plots we suggest a smaller exchange coupling of the grains in sample A as compared to sample B.