NUCLEAR ORIENTATION OF MN AND CO IN SPIN-GLASS AND REENTRANT AUFE

Low-temperature nuclear orientation has been used to study the magnetic behaviour of Mn-54 and Co-57 impurities in the AuFe alloy, below (14 at.% Fe-spin-glass state) and above (18 at.% Fe-re-entrant state) the percolation threshold. The anisotropy of the gamma-rays was monitored in the direction of the external magnetic field, as a function of the external magnetic field B-ext up to 8.5 T and of the temperature in the range 4-40 mK. In Au86Fe14 we have found total misalignment of the Mn and Co spins when B-ext --> 0 and a rather easy alignment of Mn and Co with the application of B-ext, which is typical for a spin-glass behaviour. On the other hand, both Mn and Co spins in Aus(82)Fe(18) show an alignment (mean value similar to 32 degrees), even at B-ext --> 0, and are turned only slowly by B-ext which corresponds to the re-entrant state. The difference in the Mn and Co results can be interpreted as an indication of the existence of local correlations between the Fe spins, supporting the necessity of using the finite-range model for the re-entrant state.