Magnetic properties and hyperfine interactions in amorphous Fe-Zr alloys

Amorphous ${\mathrm{Fe}}_x{\mathrm{Zr}}_{100-x} \left(20\mathrm{}\le x\le 93\right)$ samples were prepared with a high-rate sputtering technique and systematically studied using ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy. Below a critical Fe concentration of $x_c\approx 45$, magnetic order does not occur due to the loss of the Fe moment. Instead, superconductivity with reasonably high transition temperatures appears. Above $x_c$, a maximum in the magnetic ordering temperature ($T_c$) was found at $x_p\simeq 85$. At higher Fe concentrations, $T_c$ decreased and an extrapolation to $x=100\mathrm{}$ yielded an estimate of $T_c$ in pure amorphous Fe of about 200 K. Measurements of the effective hyperfine field ($H_{\mathrm{eff}}$) and the distribution of hyperfine fields [$P\left(H\right)\mathrm{}$] were also carried out. The effective hyperfine field was found to increase monotonically with the Fe concentration, unlike the values of $T_c$, and therefore indicates a monotonically increasing value of the Fe moment. These characteristics are consistent with a localized-moment description of the magnetism in which an antiferromagnetic exchange component appears at high Fe concentrations. The concentration dependence of the electric quadrupole splitting and the isomer shift were also obtained. The former shows a large difference betweeen Fe-rich and Zr-rich samples. In the latter case, the semiempirical model of Miedema and van der Woude was found to be in qualitative agreement with the data.