Influence of charge carriers on magnetic order in lightly doped manganites, detected by mu SR: Evidence for a superparamagnetic transition to the antiferromagnetic state

We detected two spontaneous precession frequencies in antiferromagnetic pur e LaMnO3, the end member of different families of charge-doped manganites. The muon site and local field orientation are identified for one frequency, which provides a measure of the staggered magnetization. We present additi onal zero and longitudinal field muon relaxation data on an LaMnO3.045 samp le in which a new regime appears above an intermediate temperature T*, wher e regions of magnetic order coexist with domains of fluctuating moments. Th ese results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix.