Raman and infrared-active phonons in hexagonal HoMnO₃single crystals: magnetic ordering effects

Abstract

Polarized Raman scattering and infrared reflection spectra of hexagonal\nHoMnO$_3$ single crystals in the temperature range 10-300 K are reported.\nGroup-theoretical analysis is performed and scattering selection rules for the\nsecond order scattering processes are presented. Based on the results of\nlattice dynamics calculations, performed within the shell model, the observed\nlines in the spectra are assigned to definite lattice vibrations. The magnetic\nordering of Mn ions, which occurs below T$_N$=76 K, is shown to effect both\nRaman- and infrared-active phonons, which modulate Mn-O-Mn bonds and,\nconsequently, Mn exchange interaction.\n