New Mössbauer-Effect Measurements onFe57in a Ni Host: The Critical Exponentβfor Ni

Abstract

We have made new Mössbauer-effect measurements on $\mathrm{Ni}{}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in order to determine whether the results of Howard, Dunlap, and Dash in the critical region can be reproduced. We have used a longitudinally magnetized source foil in order to suppress the $\Delta m=0\mathrm{}$ hyperfine components, and have in this way increased our sensitivity near $T_c$ by a factor of 5. We find that $\beta =0.378\mathrm{}\pm 0.010$ for $3\times {10}^{-4\mathrm{}}\le 1-\frac{T}{T_c}\le 4\times {10}^{-2\mathrm{}}$, with no indication of the double-valued behavior seen by Howard et al. Our result is in excellent agreement with recent perturbed-angular-correlation measurements on $\mathrm{Ni}{}_{}{}^{100}{}_{}{}^{}\mathrm{Rh}$ by our group, as well as previous determinations of $\beta$ using a scaling equation of state. With the present work, it is possible to assert that all double-valued results for $\beta$ in Ni have either been withdrawn or placed in serious doubt by subsequent work, and that the remaining experimental results cluster closely around $\beta =0.38\mathrm{}$, in good agreement with static scaling laws.