Static and dynamical critical fluctuations in disordered ferromagnets

The critical properties of the amorphous (Fe1-xMnx)75P16B6Al3 system have been investigated by small angle and inelastic neutron scattering. These alloys were previously characterized as reentrant spin-glasses with a transition to ferromagnetism at Tc and anomalies of spin-glass character at lower temperature. The aim of the study is to investigate the evolution of the critical properties as the ferromagnetic character decreases by varying x, namely by approaching the transition to true spin-glass at xc=0.35. The static exponent ν keeps the expected 0.7 value for 3d Heisenberg systems even in the strongly frustrated alloy x=0.3. By contrast dynamical scaling predicted by theory is not obeyed even for x=0.247. 4 figs., 8 refs