Low-field susceptibility measurements on a Au-Fe spin glass

DC magnetisation as well as complex AC susceptibility (0.65<or=v<or=1700 Hz) measurements have been performed in a SQUID magnetometer on the crystalline metallic spin glass Au-8 at.% Fe. The 'cusp' of the in-phase component of the susceptibility, chi ', at the spin-glass freezing temperature T g approximately=27K shows a relative temperature dependence of Delta T g /T g approximately=0.010 per decade of frequency increase. An out-of-phase component of the susceptibility, chi ", exists below T g and the magnitude of chi " increases weakly with increasing frequency. The fundamental relation chi "=( pi /2) delta chi '/ delta 1n nu derived from the general assumption of a wide spectral distribution of relaxation times is excellently obeyed and indicates that a wide spectrum of relaxation times still persists well below T g . The relaxation times are analysed in terms of the Vogel-Fulcher form 1/ tau =f 0 exp(-E/k(T-T 0 )), where f 0 approximately=10 10 s -1 , E/k approximately=30K and T 0 approximately=25.4K give consistent results for the AC susceptibility data. A breakdown of the Vogel-Fulcher law is predicted at very long observation times ( nu approximately=3*10 -4 Hz) indicated by the 'cusp' of the in-field cooled DC magnetisation curve which occurs at T g =26.4K. The 'cusp' of the DC curve is interpreted to arise from the onset of local ordering where the ordered regions at T g possibly percolate through but do not fill the whole volume of the sample.