Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7

TL;DR

This paper reports on the discovery of unidirectional terahertz light absorption in CaBaCo4O7 due to magnetoelectric resonance, revealing new insights into spin excitations in a multiferroic compound.

Contribution

It demonstrates unidirectional light absorption caused by magnetoelectric resonance in CaBaCo4O7, a novel phenomenon in this type of multiferroic material.

Findings

Identification of two magnon branches: electric dipole allowed and magnetoelectric resonance.

Observation of unidirectional light absorption linked to magnetoelectric coupling.

Temperature and magnetic field dependence of magnon modes elucidate spin excitation properties.

Abstract

Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.