New bulk amorphous Fe-(Co,Ni)-M-B (M=Zr,Hf,Nb,Ta,Mo,W) alloys with good soft magnetic properties

We have found that an amorphous phase with a wide supercooled liquid region reaching 85 K before crystallization is formed in Fe-(Co, Ni)-(Zr, Nb, Ta)-B, Fe-Co-(Zr, Nb)-(Mo, W)-B and Co-Fe-Zr-B systems. The high stability of the supercooled liquid enabled the production of bulk amorphous alloys with diameters up to 5 mm by copper mold casting. These amorphous Fe-(Co, Ni)-M-B alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.95 to 1.1 T, low coercivity of 1 to 8 A/m, Curie temperature of 560 to 590 K and low magnetostriction of 8-14×10^-6. The effective permeability of the Co-based alloys exceeds 25 000 at 1 kHz and keeps high values above 5000 at the high frequency of 1 MHz. The permeability at 1 MHz is much higher than those for any kinds of soft magnetic materials. The frequency at which the imaginary part of permeability shows a maximum is also about 1 MHz. The success of synthesis of new Fe- and Co-based amorphous alloys with good soft magnetic properties and high glass-forming ability is promising for future development of a new type of soft magnetic material.