Critical magnetic properties of the re-entrant amorphous ferromagnet Ni80-xFexB₁₂Si₈

The critical magnetic properties of the amorphous Ni-Fe-B-Si system have been studied using AC susceptibility techniques. Alloys of the composition Ni 80-x Fe x B 12 Si 8 with x>or=5 show re-entrant ferromagnetic behaviour. The critical exponents gamma , associated with the magnetic susceptibility, and delta , associated with the critical isotherm, have been determined. Values of the exponents are consistent with those predicted for three-dimensional Heisenberg systems. The critical susceptibility of the alloy with x=4 in the region above the spin-glass transition is found to follow a power law with an exponent gamma ' 0 =1.5.