Magnetic properties of (Nd,Dy)-(Fe,Co)-B-Nb and Nd-(Fe,Co)-B magnets made by the melt-spinning method with grooved and ceramic-coated roll

A new method of melt spinning using grooved and ceramic-coated chill rolls was developed. The rolls have a great effect on improving magnetic properties, which can be attributed to the achievement of a fine and uniform microstructure in the ribbons. Such rolls decrease the heat transfer coefficient at the contact surface of rolls and ribbons´, and make the cooling rate of the ribbons uniform. Since the trapped atmospheric gas between the rolls and the ribbons expelled along the grooves, the occurrence of coarse grains was prevented. Using this method, Nb-added nanocomposite magnets were produced. The Nb addition had the effect of grain refinement and enhancing the magnetic properties. The maximum (BH)_max of resin bonded magnets reached as high as 117 kJ/m³ (14.7 MGOe). Nd₂Fe₁₄B single-phase magnets were also produced and showed excellent properties.