Temperature dependence of the hall effect in amorphous Ni-Si-B alloys between 1.5 and 290 K: Evidence for magnetic ordering near a resistance minimum

The Hall effect in the metallic glasses Ni₇₆Si₁₂B₁₂, Ni₇₈Si₈B₁₄ and Ni₈₀Si₁₀B₁₀ has been measured as a function of temperature (1.5 ≤ T ≤ 290 K) and magnetic field (B ^<_～ 1.2 Tesla). At room temperature the Hall resistivity ρ_H is negative and depends linearly on the magnetic field for all three compositions. With decreasing temperature Ni₈₀Si₁₀B₁₀ exhibits a negative spontaneous Hall coefficient and a transition to ferromagnetism at about 110 K. In case of Ni₇₆Si₁₂B₁₂ and Ni₇₈Si₈B₁₄ an anomalous part contributes below ～ 40 K and ρ_H changes from negative to positive sign at about 9 K. For these two alloys we find that the initial slope of the ρ_H(B) curves follows a Curie-Weiss law with Tθ ≈ 0 K and the anomalous contribution of the Hall resistivity can be described by a Brillouin function for superparamagnetism.