Magnetic properties of novel resin-bonded exchange coupled rare-earth magnets

The magnetic properties of compaction-molded resin-bonded magnets which exhibit exchange spring behaviour have been measured. The starting compositions of the alloys were Nd_4.5Fe₇₃B_18.5Co₃Ga₁ and Nd_3.5Dy₁Fe₇₃B_18.5Co₃Ga₁ and the preparation method consisted of melt-quenching followed by annealing for a short period. The magnets have remanent magnetisation approximately 70% of saturation magnetisation. The variation of the magnetic properties with temperature in the range 250-320 K has been investigated and magnetic viscosity measurements have been made. These data are compared with those from a conventional resin-bonded NdFeB-type permanent magnet. It has been found that the exchange coupled materials have smaller variations in magnetic properties over the temperature range investigated, and they exhibit less time dependence of magnetisation, compared with the conventional material.