Mössbauer study of amorphous ${\mathrm{Fe}}_{81}$${\mathrm{B}}_{13.5}$${\mathrm{Si}}_{3.5}$${\mathrm{C}}_2$

Amorphous alloy ${\mathrm{Fe}}_{81}$ ${\mathrm{B}}_{13.5}$ ${\mathrm{Si}}_{3.5}$ ${\mathrm{C}}_2$ (METGLAS® 2605SC) in ribbon form has been investigated from 4.2 to 706 K with the use of transmission Mössbauer spectroscopy. The Curie temperature, $T_F$, is 668 K. The average hyperfine field, $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$, has a temperature dependence given by $\frac{H_{\mathrm{hf}}\mathrm{}\left(T\right)-H_{\mathrm{hf}}\mathrm{}\left(0\right)\mathrm{}}{H_{\mathrm{hf}}\mathrm{}\left(0\right)\mathrm{}}=-B_{\frac{3}{2}}{\left[\frac{T}{T_F}\right]}^{\frac{3}{2}}-C_{\frac{5}{2}}{\left[\frac{T}{T_F}\right]}^{\frac{5}{2}}$ for $\frac{T}{T_F}<0.9\mathrm{}$ with $B_{\frac{3}{2}}=0.30\mathrm{}\pm 0.05$ and $C_{\frac{5}{2}}=0.29\mathrm{}\pm 0.05$; hence spin-wave excitation is indicated. Temperature dependences of the hyperfine field and average linewidth suggest that the exchange-constant distribution is small. The quadrupole splitting above $T_F$ ranges between 0.35 and 0.51 mm/s. The average quadrupole shift below $T_F$ is zero; thus the magnetic hyperfine field is randomly oriented with respect to the principal axes of the electric field gradient in this temperature region. The temperature dependence of the spectrum shift can be described by the Debye theory of atomic vibrations. Analysis of data on the spectrum shift and recoilless fraction at low temperatures may imply that atoms in the as-quenched alloy lie in potential wells with double potential minima.