Influence of charge carriers on magnetic order in lightly doped manganites, detected by MuSR: evidence for a first order transition to the antiferromagnetic state

We detected two spontaneous precession frequencies in antiferromagnetic pure 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 additional zero and longitudinal field muon relaxation data on an LaMnO3.045 sample in which a new regime appears above an intermediate temperature T*, where regions of magnetic order coexist with domains of fluctuating moments. These results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix.