• The Raman spectra of LuMnO 3 and YMnO 3 reveal broad peaks near ∼800 cm −1 and ∼770 cm −1 , respectively, below the Néel temperature, and they are attributed to 180° spin-rotational excitations of the Mn 3+ trimers. • Both LuMn 1−x Fe x O 3 and YMn 1−y Al y O 3 systems show suppression of the spin-rotational excitation peak intensity with no change in the peak wavenumber supporting that the spin excitations are from the Mn-ion trimers unaffected by the substitution. • Two-dimensional correlation spectroscopy (2D-COS) analysis demonstrates that the 180° spin-rotational excitation peak is not a single broad peak but is consisted of multiple overlapping components with energy separations of ∼meV. • The discrete components of the spin excitation peak suggest that the spin-rotational excitations are related with multiple states with discrete energy differences ∼meV near the ground state and the spin-rotated state. Spin-rotational excitations in hexagonal R MnO 3 ( R = rare-earths, Y) are believed to be due to localized rotations of the Mn 3+ spins in the triangular lattice through the resonance with the Mn d-d transition of the incident and/or scattered photons in the Raman scattering process. In this study, we confirmed experimentally that the spin-rotational excitations are localized within the undisturbed Mn-ion trimers, by comparing the LuMn 1−x Fe x O 3 (magnetic Fe-ion substitution) and YMn 1−y Al y O 3 (non-magnetic Al-ion substitution) systems. Analyses using the two-dimensional correlation spectroscopy (2D-COS) revealed that the spin-rotational Raman peaks consist of multiple overlapping components rather than being single broad peaks. Variations in the spin–spin integral J and effective S values due to imperfections and substitution would be continuous so that they may lead to a single broad peak. Therefore, existence of the multiple components is an important finding in understanding the nature of the spin-rotational excitations. The new finding suggests the possibilities of multiple states with discrete energy differences ∼meV near the ground state and the spin-rotated state which are transient states excited during the steady-state resonance Raman scattering process in the anti-ferromagnetically ordered state of the hexagonal R MnO 3 ( R = Lu, Y) systems
Lee et al. (Fri,) studied this question.