Magnetic properties of amorphous Fe4Ni74Si9B13

Abstract 57 Fe Mossbauer effect measurements have been performed on the amorphous spin-glass alloy Fe 4 Ni 74 Si 9 B 13 . Magnetic hyperfine-split spectra are found below an average magnetic transition temperature T f ≈ 11 K , the transition being not sharp but smeared over several degrees. In the spin-glass phase the hyperfine field H int near saturation has an average value of (230±5) kOe and shows a distribution P ( H ) which is zero for H ⪅ 140 kOe. The most probable hyperfine field is found to follow the relation H int ( T )=(260 kOe)·(1 − T / T f ) β over a large temperature range, with β =0.40. An external magnetic field strongly effects the spin orientation in the spin-glass phase. For T > T f and in the presence of an external field our measurements indicate that superparamagnetic clusters exist at least up to 77 K, with an average cluster moment of about 70 μ B .