Hyperfine Interactions 34 (1987) 467-470 467 MOSSBAUER STUDY OF MAGNETIC CRITICAL BEHAVIOR OF Feo.s7sVo.12 s X.S. CHANG and C. HOHENEMSER Department of Physics, Clark Universi~ Worceste~ MA ~ U&A. The disordered alloy Fel_xVx has a well defined maximum in T c at x = 0.125. Working at this value to suppress T c broadening, we have made high precision M6ssbauer measure- ments in the ferromagnetic region. When analyzed in terms of four hyperfine field components our spectra suggest that the sample is annealed. Fitting the hyperfine field over reduced temperatures 1.7x10 -3 < t < 5x10 -I with corrections to scaling yields ~ =0.362(8), in agreement with earlier work on pure Fe, and with Fisher's predic- tions for annealed disordered systems. Hyperfine interactions have produced some of the most precise and reliable measurements of magnetic critical behavior in metals. The best results are confined to pure or dilute impurity/host systems in which impurity-impurity interactions are absent or weak /I/. Because impurities disturb critical behavior in various ways /2/, it is of interest to extend hyperfine methods to the study of disordered alloys. This leads, however, to two kinds of inhomogeneity which interfere with the analysis of intrinsic critical behavior. Macroscopic or chemical inhomogeneity, due to gradients in the concentration, x, produces T c smearing because in general dTc/dx = 0 Microscopic inhomogeneity, due to variable local atomic environments, makes interpretation of hyperfine spectra difficult and nonunique. In many cases both kinds of inhomogeneity are present. The recent review of quenched magnetic alloys by Kaui /3/ lists many such cases. In past work by our group /2/ macroscopic inhomogeneity was overcome by choosing small x and dTc/dX, as in work on Fel_xAlx with 0 < x < 0.04. In the present paper we discuss measurements on Fel_xV x for which concentration gradients are suppressed by choosing dTc/dX = 0, a condition satisfied at x = 0.125. As we have demonstrated /4/ this strongly suppresses macroscopic inhomogeneity effects, and produces a transition as sharp as that of pure Fe /2,5/. Samples. Our M6ssbauer absorber was made via rapid quenching of arc melted solutions to room temperature, using 4N Fe and 3N V. Macroscopic homogeneity was checked via electron microprobe analysis, and showed that chemical composition varied by less than 0.5 at. % over the thickness of the sample foil. X-ray diffraction data and the distinct side band structure of the M6ssbauer spectra at room temperature indicate that the sample is crystalline and microscopically homogeneous. Experiment~l. We used a two stage oven as described earlier /4/, with a temperature drift of less than 0.05 K per day. For quick and accurate checks of T c we employed a constant velocity drive to measure the centroid velocity transmission (CVT) /4/. Alternatively, we found T c via power law fits to the hyperfine field (see below). The two methods were consistent to within experimental error. By taking several CVT scans during a given critical exponent measurement 9 J.C. Baltzer A.G., Scientific Publishing Company