μSR investigation of the magnetic ordering in EuAs3

We have investigated the magnetic ordering and the incommensurate–commensurate phase transition in EuAs3 by zero-field (ZF) and longitudinal-field μSR. In the commensurate phase, stable at temperatures below TL=10.3 K, the ZF muon signal exhibits oscillations corresponding to four muon precession frequencies the lowest of which behaves anomalously. The muon signal shows no oscillation but exponential decay in the incommensurate phase stable in temperature range from TL≈10.3 K up to TN≈11 K. The temperature dependence of the fitted relaxation rate shows divergence-like behaviour at the ordering temperature TN≈11 K and also at the lock-in transition TL≈10.3 K. The results are in qualitative agreement with those previously obtained by neutron and X-ray magnetic scattering investigations except for the anomalous temperature dependence of the lowest frequency in the commensurate phase. We propose a model for this anomalous behaviour.