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We determined the paramagnetic critical scattering of the reentrant ferromagnets Au1−xFex, with x=0.2, 0.18, and 0.16, i.e., close to the threshold (xc∼0.155), below which ferromagnetism disappears and a spin-glass state sets in. Following the Ornstein–Zernicke formalism, we derived the inverse critical ferromagnetic correlation length (κ=ξ−1) and the related magnetic susceptibility. The macroscopic susceptibility χq=0 of the samples was also determined in a separate experiment with a Faraday balance. The neutron results show the same behavior of critical type with χq=0 for x=0.18 but not for x=0.16. We interpret this discrepancy as an indication for a non-well-defined ferromagnetic transition for x=0.16. A further comparison of our results with those for Fe shows that the amplitude of the correlation length increase with increasing disorder so that, at the same reduced temperature τ, the correlations are much larger in the disordered samples than in Fe. As a consequence of this, the ferromagnetic correlations in the disordered samples persist well above Tc and lead to a much wider critical region than is the case in Fe and in usual ferromagnets. © 1996 American Institute of Physics.
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