Understanding the magnetic dynamics and magnetostructural coupling in the paramagnetic phase of TbMnO3 by muon-spin spectroscopy

In this work we present a comprehensive study of the spin dynamics and fluctuations in the ordered magnetic phases of the prototype multiferroic material TbMnO3. From the temperature dependence of the dynamical and static components of the time-dependent asymmetry, we demonstrate the existence of strong local magnetic-field disorder arising from the modulated Mn3+ spin arrangement and the effect of the Tb3+ ordering at low temperatures. We provide evidence for an unusual magnetostructural coupling in the paramagnetic phase of TbMnO3 by means of muon spin spectroscopy. No short-range magnetic ordering definitively occurs in the paramagnetic phase and the unusual properties found in the temperature dependence of the magnetic susceptibility are due to a magnetostructural coupling, likely involving oxygen displacements.