Staggered magnetization, critical behavior and weak ferromagnetic propert ies of LaMnO${}_3$ by muon spin rotation

We present a study of a microtwinned single crystal of LaMnO${}_3$ by means of implanted muons. Two muon stopping sites are identified from the symmetry of the internal field in the ordered phase. The temperature dependence of these fields yields the behavior of the staggered magnetization from which a static critical exponent ($\beta =0.36(2)$) is extracted and discussed. The muon spin-spin relaxation rate shows a critical slowing down (contrary to preliminary findings) with a critical exponent $n=0.7(1)$, witnessing the Ising nature of the dynamic fluctuations. The muon precession frequencies vs. applied magnetic field reveal the saturation of the weak ferromagnetic domain structure originated by the Dzialoshinski-Moriya antisymmetric exchange.