Spin freezing in the kagome system SrCr8Ga4O19 - high resolution study of the elastic and low-energy dynamic responses

The magnetic response of the SrCr8Ga4O19 compound has been examined using t he backscattering instrument IN16 at the ILL, in the temperature range from 100 mK up to 20 K. Both the standard configuration with an energy resoluti on of Delta E approximate to 1 mu eV, and the polished monochromator config uration with Delta E approximate to 0.4 mu eV were used to examine the resp onse in an energy window extending to +/- 14 mu eV. Additional data taken o n INS have been used to investigate the effect of the energy resolution wid th on the observed 'elastic' signal. The apparent transition temperature be comes independent of the resolution for Delta E < 1 mu eV, and with a resol ution of Delta E = 0.4 mu eV there is no detectable broadening of the elast ic peak at temperatures below about T less than or equal to 2 K. Our observ ations are in overall agreement with the earlier results on the elastic res ponse, confirm the freezing of about 1 of the total Cr (S = 3/2) moment and push the time scale of the frozen configuration into the 0.1 mu s range. ( C) 1999 Elsevier Science B.V. All rights reserved.