Iron� High Magnetic Field Behavior of Impurities Chromium� In

THE PRESENCE of small amounts of iron in chromium metal results in a lowering of the Neel temperature along with other anomalous diagram[l, changes in the phase r 1 , 2]. Suscepti­[I] N eel bility measurements 1 below the tem­perature show that the iron sites have associ­ated with them localized magnetic moments of about 1·4f.LIJ I· per iron atom and that the iron moments remain paramagnetic down to low temperatures (2°K for 1I% Fe in Cr). Para­magnetic resonance of the iron impurities in Cr have shown[3] [ that the iron moment is in fact localized and that the exchange field acting on the Fe sites at OaK is ~ 4 kOe. The Mossbauer effect in ·>7Fe has been used to study the hyperfine interactions at the Fe sites in dilute Cr-Fe alloysr4, 5J: most recent­ly a comprehensive work was reported by Herbert el al.[6] who suggested a model for the iron moments in which an exchange field of 225 kOe arising from the chromium spin density wave (SDW) acts on the iron sites, while at the same time there is a partial spin compensation of the Fe moments having a characteristic temperature of 60°K. In this note we present some additional hyperfine field data which are relevant to the problem and suggest that an alternate model due to ('{ .[6J Housley and Dash [7] might also be used to understand the hyperfine interactions in this system. The Mossbauer measurements were made using a 5 7CO C in Cr source vs. a single line absorber and with a 0·5% Fe in Cr absorber vs. a narrow line source. At room temperature the 57CO in Cr source linewidth was 0·23 mm/sec, while i% the ! Fe in Cr absorber linewidth was 0·31 mm/sec. The measure­ments may be summarized as follows: (a) the line broadens as T decreases until at 4·2°K the spectrum is consistent with a magnetic hyperfine field distribution centered at about 35 kOe; (b) in an applied field Ho, the spectra become resolved at about Ho = 40 kOe, the splitting increases with increasing Ho• and the lines remain broad; (c) polarization measurements in the external field show that the total net field at the nucleus Hn is positive (i.e. in the same direction as Ho). Il