Magnetic Properties of Nd18Fe76B6 and (Nd,Dy)18Fe75B6Ga1, Hot Pressed Magnets Using Melt Spun Ribbons

The magnetic properties of hot pressed magnets made from melt spun ribbons depends on the microstructure of the initial ribbons and on the conditions during pressing. For hot pressed magnets made from Nd₁₈Fe₇₆B₆ alloy ribbons spun at a roll speed of 16 m/sec pressed for 2-5 minutes at 650-700 °C, a high density (7.41 g/cm³) is achieved. The remanence (J_r ∼0.88 T) and maximum energy product ((BH)_max ∼132 kJ/m³) are substantially enhanced over values predicted for isolated non-interacting particles. This may be due to nanoscale grains and/ or to a partial alignment of the grains with easy direction parallel to the press direction. For hot pressed magnets made from (Nd,Dy)₁₈Fe₇₅B₆Ga₁ ribbons, it is interesting to note that the coercivity (>2400 kA/m) achieved after hot pressing at 700 °C is still higher than those for Dy containing (∼2400 kA/m) and ternary NdFeB melt spun ribbons which have a maximum coercivity of 1834 kA/m. The remanence increases probably due to some alignment of hard magnetic grains but has a low value as compared to that of the ternary alloy. The maximum energy product for the hot pressed magnets is higher than that of as quenched ribbons due to higher remanence and better second quadrant B-H curve.