Charge/orbital and antiferromagnetic ordering in LaSr2Mn2O7

First mu SR results for the bilayercd manganite LaSr2Mn2O7 are reported. We have studied the effect on the relaxation rates of the charge/orbital and antiferromagnetic ordering. Between the charge/orbital ordering temperature (T-CO = 220 K) and the antiferromagnetic transition temperature (T-N = 170 K), unexpected hysteretic behaviour and field history dependence of the re laxation rates were observed. The field history dependence is observed by i ncreased zero-field relaxation rates after switching the external field on and off again. These effects suggest field induced and residual magnetic co rrelations above T-N which are presumably related to the formation of magne to-elastic polarons. No precession signal was observed for T < T-N, the onl y signature of the magnetic transition bring the almost complete loss of as ymmetry reflecting the wide field distribution at the muon site. (C) 2000 E lsevier Science B.V. All rights reserved.