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 the backscattering instrument IN16 at the ILL, in the temperature range from 100 mK up to 20 K. Both the standard configuration with an energy resolution of Delta E approximate to 1 mu eV, and the polished monochromator configuration with Delta E approximate to 0.4 mu eV were used to examine the response in an energy window extending to +/- 14 mu eV. Additional data taken on INS have been used to investigate the effect of the energy resolution width on the observed 'elastic' signal. The apparent transition temperature becomes independent of the resolution for Delta E < 1 mu eV, and with a resolution of Delta E = 0.4 mu eV there is no detectable broadening of the elastic peak at temperatures below about T less than or equal to 2 K. Our observations are in overall agreement with the earlier results on the elastic response, 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.