Magnetic and magnetoelectric excitations in TbMnO$_3$

TL;DR

This study investigates magnetic and magnetoelectric excitations in TbMnO3, revealing that electromagnons and antiferromagnetic resonances are related and can be excited by magnetic fields, with detailed behavior under varying conditions.

Contribution

The paper demonstrates that electromagnons in TbMnO3 are excited by magnetic fields and share modes with AFMR, providing new insights into multiferroic excitations.

Findings

Electromagnons and AFMR coincide in frequency.

Electromagnons can be excited by magnetic ac-fields.

Distinct fine structures appear under magnetic fields and low temperatures.

Abstract

Magnetic and magnetoelectric excitations in the multiferroic TbMnO_3 have been investigated at terahertz frequencies. Using different experimental geometries we can clearly separate the electro-active excitations (electromagnons) from the magneto-active modes, i.e. antiferromagnetic resonances (AFMR). Two AFMR resonances were found to coincide with electromagnons. This indicates that both excitations belong to the same mode and the electromagnons can be excited by magnetic ac-field as well. In external magnetic fields and at low temperatures distinct fine structure of the electromagnons appears. In spite of the 90^o rotation of the magnetic structure, the electromagnons are observable for electric ac-fields parallel to the a-axis only. Contrary to simple expectations, the response along the c-axis remains purely magnetic in nature.