Resistivity of amorphous ferromagneticFecAu1−calloys: Anisotropy and field dependence

Owing to their spontaneous magnetization, amorphous ferromagnetic metals exhibit a direction of preference. Hence, the electrical resistivity is anisotropic and consists of three main components: the longitudinal resistivity ${\rho }_{\parallel }$, the transverse resistivity ${\rho }_{\perp }$, and the spontaneous Hall resistivity ${\rho }_H\mathrm{}\left(0\right)\mathrm{}$. These contributions also show a distinct dependence on the applied magnetic field. In this article, we present our experimental studies of the amorphous ferromagnetic alloy system ${\mathrm{Fe}}_c{\mathrm{Au}}_{1-c}$ ($0.45\le c\le 0.97$). Most of the measured variables show a pronounced concentration dependence above $c=0.9\mathrm{}$. This is correlated with the sudden drop of the magnetic moment of the Fe atoms above $c=0.9\mathrm{}$. The high-field Hall effect in principle allows a determination of the effective number of conduction electrons. In the discussion we generalize the single-site approximation for the resistivity of amorphous and liquid transition metals to amorphous ferromagnets. In the framework of the phase-shift treatment of the resistivity, the spin-up and spin-down conduction electrons are scattered according to different phase shifts ${\rho }_2^{\uparrow }$ and ${\rho }_2^{\downarrow }$. Numerical calculations of the resistivity are performed and demonstrate the strong sensitivity of the calculated $\rho$ on the various parameters. The anisotropy effects are semiquantitatively discussed by extension of a model due to Fert and Jaoul.