THz and infrared studies of multiferroic hexagonal Y_(1-x)Eu_xMnO_3 (x=0 - 0.2) ceramics

TL;DR

This study investigates the THz and infrared properties of multiferroic hexagonal Y_(1-x)Eu_xMnO_3 ceramics across a wide temperature range, revealing strong spin-lattice coupling and characteristic magnetic resonance behaviors.

Contribution

It provides new insights into the spin-lattice interactions and magnetic excitations in Eu-doped hexagonal YMnO_3 ceramics using spectroscopic techniques.

Findings

Identification of a kink in permittivity near T_N indicating spin-lattice coupling

Observation of antiferromagnetic resonance peaks at 43 and 73 cm-1

Weak phonon softening and permittivity increase at high temperatures

Abstract

We report an investigation of hexagonal Y_(1-x)Eu_xMnO_3 ceramics with x=0, 0.1 and 0.2 using infrared and THz spectroscopies in the temperature range between 5 and 900 K. The temperature dependence of the THz permittivity reveals a kink near the antiferromagnetic phase transition temperature T_N ~ 70 K giving evidence of a strong spin-lattice coupling. Below T_N two absorption peaks were revealed in the THz spectra close to 43 and 73 cm-1. While the first peak corresponds to a sharp antiferromagnetic resonance exhibiting softening on heating towards TN, the second one may be attributed to an impurity mode or a multiphonon absorption peak. High-temperature THz spectra measured up to 900 K reveal only small gradual increase of the permittivity in agreement with a weak phonon softening observed in the infrared reflectance spectra upon heating. This corresponds to an improper ferroelectric character of the phase transition proposed from first principle calculations by Fennie and Rabe [Phys. Rev. B 72 (2005), pp. 100103(R)].