A neutron scattering investigation of a Au-Fe spin glass alloy

Neutron scattering measurements on a Au-Fe alloy containing 10 at.% Fe have been made using two different techniques which together help to illuminate some interesting dynamical properties of the spin glass alloy system. Time-of-flight measurements of the scattering function S(q,ω) reveal a broad, q-dependent, quasi-elastic line and a central elastic peak which at high temperatures is due mainly to the nuclear incoherent scattering from the sample. The line width of the quasi-elastic spectrum diminishes gradually with decreasing temperature, appears to go through a minimum especially at the higher q-values but always remains finite as T→0K. Below some relatively high temperature the integrated quasi-elastic scattering intensity begins to decrease with decreasing temperature accompanied by a continuous increase of the elastic scattering intensity. The static susceptibility chi(q) obtained from the broad quasi-elastic spectrum has a maximum which occurs at a temperature a little higher than that observed in the low field a.c. susceptibility. On the other hand measurements at very low q-values (0.005<q<0.03A-1) of the total scattering cross-section (which is mainly quasi-elastic) shows a series of q-dependent maxima at lower temperatures which extrapolate smoothly as q→0 to the temperature of the maximum in the a.c. susceptibility. We believe the results demonstrate the gradual process of freezing of spins over a wide temperature range and also reveal the presence of relatively rapid dynamical fluctuations in the spin system at low temperatures. (author)