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

Abstract

The orthorhombic rare-earth manganite compounds R MnO _3 show a global magnetic order for $T\lt {T}_{N}$ , and several representatives are multiferroic with a cycloidal spin ground state order for $T\lt {T}_{{\rm{cycl}}}\lt {T}_{N}\approx 40\,{\rm{K}}$ . We deduce from the temperature dependence of spin–phonon coupling in Raman spectroscopy for a series of R MnO _3 compounds that their spin order locally persists up to about twice T _N . Along the same line, our observation of the persistence of the electromagnon in GdMnO _3 up to $T\approx 100\,{\rm{K}}$ is attributed to a local cycloidal spin order for $T\gt {T}_{{\rm{cycl}}}$ , 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.

Keywords

• RMnO3
• multiferroics
• electromagnon
• Raman spectroscopy
• spin–phonon coupling