New bulk amorphous magnetic materials

The relationship between structure and magnetic properties of the melt-spun ribbons with thicknesses up to 200 mum and rods having up to 3mm diameter prepared by mould casting and suction casting techniques, of nominal compositions Fe56Co7Ni7Zr6M1.5Nb2.5B20 (M = Zr, Ti, Ta or Mo) and Nd50Fe40Si10-x was investigated. Saturation magnetisations up to 1.1 T, coercive fields of about 5 A/m, magnetic permeabilities of 25 000-30 000 in the as-cast state were measured for the Fe-based amorphous alloys. The large values over 300 kA/m of the intrinsic coercive field at room temperature and over 600 kA/m at 200 K measured in low magnetic fields for the Nd-Fe-based "X-ray amorphous" alloys. and its dependence on temperature and cooling rate are ascribed to the existence of very small ferromagnetic clusters embedded in an Nd-rich matrix. The thermal treatments applied to the amorphous samples below the crystallisation temperature cause an improvement in the magnetic properties as a consequence of structural relaxation. (C) 2001 Elsevier Science B.V. All rights reserved.