The role of the rare earth in the lattice and magnetic coupling in multiferroic h-HoMnO3

TL;DR

This study uses Raman scattering to explore how the lattice vibrations and magnetic interactions in hexagonal HoMnO3 are influenced by the rare earth Ho ions, revealing their significant role in magnetic transitions and excitations.

Contribution

It provides new insights into the coupling between lattice and magnetic properties in HoMnO3, highlighting the impact of Ho ions on magnetic excitations and anisotropy.

Findings

E2 phonon mode affected by magnetic order

Ho ions influence magnetic transition behavior

Magnetic excitations linked to Mn-Ho interactions

Abstract

We used Raman scattering to study the lattice and magnetic excitations in the hexagonal HoMnO3 single crystals. The E2 phonon mode at 237 cm-1 is affected by the magnetic order. This mode is related to the displacement of Mn and O ions in a-b plane and modulates the Mn-O-Mn bond angles in a-b plane and the in-plane Mn-Mn superexchange interaction. The mode at 269 cm-1 associated to the displacement of the apical Ho3+ ions along the c direction presents an abrupt change of slope at TN showing that the role of the rare earth ions can not be neglected in the magnetic transition. We have identified magnon and crystal field excitations. The temperature dependence of the magnetic excitations has been compared to the Mn and Ho moment and indicates that the exchange interaction pattern between Mn and Ho atoms drives the uniaxial anisotropy gap above the Mn-spin-rotation transition.