Magnetic properties of a glassy ferromagnet: ${\mathrm{Fe}}_{78}$${\mathrm{B}}_{13}$${\mathrm{Si}}_9$

METGLAS $2605S2$, ${\mathrm{Fe}}_{78}$ ${\mathrm{B}}_{13}$ ${\mathrm{Si}}_9$, has been investigated over a temperature range of 77-900 K by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy. The analysis of the distribution of hyperfine fields indicates two peaks. The maximum of the dominant peak varies with temperature. Another smaller peak is centered around 100 kOe. The $\frac{H_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}}{H_{\mathrm{eff}}\mathrm{}\left(0\right)\mathrm{}}$ vs $\frac{T}{T_c}$ deviates from the Brillouin curve for spin $S=1\mathrm{}$ but agrees well with the modified Handrich's expression proposed earlier by Prasad et al. The temperature dependence of the average hyperfine field $H_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}$ can be described well by $H_{\mathrm{eff}}\mathrm{}\left(T\right)=H_{\mathrm{eff}}\mathrm{}\left(0\right)\mathrm{}$ [$1-B_{\frac{3}{2}}{\left(\frac{T}{T_c}\right)}^{\frac{3}{2}}-C_{\frac{5}{2}}{\left(\frac{T}{T_c}\right)}^{\frac{5}{2}}$] with $H_{\mathrm{eff}}\mathrm{}\left(0\right)=276\mathrm{}$ kOe, $B_{\frac{3}{2}}=0.23\mathrm{}$, and $C_{\frac{5}{2}}=0.32\mathrm{}$ for $\frac{T}{T_c}<0.7\mathrm{}$ indicative of the existence of spin-wave excitations. The Curie and the crystallization temperatures are found to be 733±1 K and 836±2 K by the zero-velocity counting method with the use of a heating rate of 5 K/min. The quadrupole splitting just above $T_c$ is (0.30±0.04) mm/sec whereas the average quadrupole splitting below $T_c$ is zero. The critical exponent $\beta$, in the expression $\frac{H_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}}{H_{\mathrm{eff}}\mathrm{}\left(0\right)\mathrm{}}=D{(1-\frac{T}{T_c})}^{\beta }$ is found to be 0.34±0.02 from the measurements in the...