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

Abstract

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 Tg approximately=27K shows a relative temperature dependence of Delta Tg/Tg approximately=0.010 per decade of frequency increase. An out-of-phase component of the susceptibility, chi , exists below Tg 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 Tg. The relaxation times are analysed in terms of the Vogel-Fulcher form 1/ tau =f0exp(-E/k(T-T0)), where f0 approximately=1010 s-1, E/k approximately=30K and T0 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 Tg=26.4K. The 'cusp' of the DC curve is interpreted to arise from the onset of local ordering where the ordered regions at Tg possibly percolate through but do not fill the whole volume of the sample.