Raman and Infrared-Active Phonons in Hexagonal HoMnO$_3$ Single Crystals: Magnetic Ordering Effects

TL;DR

This study investigates how magnetic ordering in hexagonal HoMnO$_3$ affects its Raman and infrared-active phonons, revealing coupling between magnetic and lattice vibrations through experimental spectra and theoretical analysis.

Contribution

It provides the first detailed analysis of magnetic ordering effects on phonons in HoMnO$_3$ using polarized Raman, infrared spectra, and lattice dynamics calculations.

Findings

Magnetic ordering at T_N=76 K influences phonon modes.

Lattice vibrations modulate Mn-O-Mn bonds and exchange interactions.

Spectral lines are assigned to specific lattice vibrations.

Abstract

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