Impact of temperature-dependent local and global spin order in RMnO3 compounds for spin-phonon coupling and electromagnon activity

The orthorhombic rare-earth manganite compounds RMnO3 show a global magnetic order for T < T-N, and several representatives are multiferroic with a cycloidal spin ground state order for T < T-cycl < T-N approximate to 40 K. We deduce from the temperature dependence of spin-phonon coupling in Raman spectroscopy for a series of RMnO3 compounds that their spin order locally persists up to about twice TN. Along the same line, our observation of the persistence of the electromagnon in GdMnO3 up to T approximate to 100 K is attributed to a local cycloidal spin order for T > T-cycl, in contrast to the hitherto assumed incommensurate sinusoidal phase in the intermediate temperature range. The development of the magnetization pattern can be described in terms of an order-disorder transition at T-cycl within a pseudospin model of localized spin cycloids with opposite chirality.