Antiferromagnetic ordering in RMnO3 rare-earth manganites observed by optical spectroscopy

The optical absorption spectra of hexagonal rare-earth manganites (RMnO₃ with R = Er, Tm, Yb) have been measured in the 5000-13,000 cm⁻¹ infrared spectral range as a function of temperature between 8 and 300 K. A series of transitions have been assigned for the trivalent rare-earth ions in trigonal crystal field. Some of the Stark components of the rare-earth multiplets split below the Néel-temperature due to antiferromagnetic ordering. The Néel-temperature for the three compounds investigated decreases with increasing ionic radius of the rare-earth ions.