Magnetic and Mössbauer investigation of amorphous (FexNi1-x)80B20alloys

A Mössbauer and magnetic study of the amorphous systems (FexNi1-x)80B20and (FexNi1-x)80B19Si1in the temperature range 4.2 - 300 K has been undertaken. Besides the average hyperfine fields at the iron sites, in three cases⁶¹Ni average hyperfine fields have also been determined. It is concluded that at high Ni concentrations the atomic magnetic moments for both Fe and Ni decrease, the latter decreasing stronger and collapsing close to Ni80B20. The ratio D/Tc, with D the spin wave stiffness constant obtained from the coefficient B of the Bloch law which describes satisfactorily the low temperature dependence of the saturation magnetization and hyperfine fields, has a rather pronounced discontinuity between 30 and 40 at% Ni, possibly due to some changes in the short range order.