Bulk amorphous alloys with soft and hard magnetic properties

This paper reviews our recent findings of bulk amorphous alloys with soft or hard magnetism at room temperature. Soft magnetic characteristics combined with large glass-forming ability (GFA) were obtained in Fe72Al5Ga2P11C6B4 and Fe72Al5Ga2P10C6B4Si1 amorphous alloys. The maximum thickness for glass formation by copper mold casting was about 3 mm. These bulk amorphous alloys have a Curie temperature (Tc) of 600–606 K in an annealed state and their soft magnetic properties are about 1.1 T for saturation magnetization (Bs) and 2–6 A m−1 for coercive force (Hc). The thick amorphous sheets up to 180 gmm in thickness exhibit high permeability of 7000–12 000 at 1 kHz. On the other hand, the hard magnetic properties were obtained for amorphous Ln60Fe30Al10 (Ln = Nd or Pr) cylinders with diameters below 15 mm. The large GFA is due to the high Tx/Tm of 0.85–0.90 and the small temperature intervals of 85–140 K between Tm and Tx. The Tc is around 600 K and typical magnetic properties are 0.13 T for remanence, 0.15 T for Bs, 280 k A m−1 for Hc and 19 kJ m−3 for (JH)max. The hard magnetic properties disappear in the crystallized state. The first success of synthesizing the ferromagnetic bulk amorphous alloys is important for future progress of basic science and applications.