Evidence for a transition from weak to strong ferromagnetism from spontaneous resistivity anisotropy and high-field magnetic susceptibility data in amorphous (Fe-Ni)₈₀ (P-B)₂₀ alloys

Abstract

The magnetoresistivity (both longitudinal and transverse) and high-field magnetic susceptibility X_hf measurements have been performed on the glassy alloy series Fe_xNi_80-xB₂₀ and Fe_xNi_80-xP₁₄B₆ (10< x< 80 at.%) at 4.2 K in fields up to 7 and 15 kOe, respectively. While the split-band model fails to account for the present results, the observed composition dependence of the spontaneous resistivity anisotropy (SRA) finds a straightforward explanation in terms of the two-current conduction model. Based on this model, the composition dependence of spin-up ρ_↑⁰ and spin-down ρ_↓⁰ residual resistivities has been computed. The computed variation of ρ_↑⁰ and ρ _↓⁰ with composition is shown to provide conclusive evidence not only for a transition from weak to strong ferromagnetism at a concentration x≈ 60 at.% in the amorphous Fe_xNi_80-xP₁₄B₆ alloy series, but also for weak ferromagnetism in Fe_xNi_80-xB₂₀ glasses in the entire composition range. The difference in the ferromagnetic behavior of the two amorphous alloy series studied here has been explained by taking into account the charge transfer from the metalloid atoms to the transition-metal d bands. These observations are further supported by the X_hf data. Furthermore, it is shown that no direct correlation exists between SRA and the saturation magnetization.