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)20alloys

The magnetoresistivity (both longitudinal and transverse) and high-field magnetic susceptibility ${\chi }_{\mathrm{hf}}$ measurements have been performed on the glassy alloy series ${\mathrm{Fe}}_x{\mathrm{Ni}}_{80-x}{\mathrm{B}}_{20}$ and ${\mathrm{Fe}}_x{\mathrm{Ni}}_{80-x}{\mathrm{P}}_{14}{\mathrm{B}}_6$ ($10<x<\mathrm{}80\mathrm{}$ 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 ${\rho }_{\uparrow }^0$ and spin-down ${\rho }_{\downarrow }^0$ residual resistivities has been computed. The computed variation of ${\rho }_{\uparrow }^0$ and ${\rho }_{\downarrow }^0$ with composition is shown to provide conclusive evidence not only for a transition from weak to strong ferromagnetism at a concentration $x\simeq 60$ at.% in the amorphous ${\mathrm{Fe}}_x{\mathrm{Ni}}_{80-x}{\mathrm{P}}_{14}{\mathrm{B}}_6$ alloy series, but also for weak ferromagnetism in ${\mathrm{Fe}}_x{\mathrm{Ni}}_{80-x}{\mathrm{B}}_{20}$ 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 ${\chi }_{\mathrm{hf}}$ data. Furthermore, it is shown that no direct correlation exists between SRA and the saturation magnetization.