Confirming the trilinear form of the optical magnetoelectric effect in the polar honeycomb antiferromagnet Co2Mo3O8

S Reschke,J Deisenhofer,D Szaller,S Bordács,O Zaharko,K Guratinder,S Ghara,L Prodan,D G Farkas,V Tsurkan,I Kézsmárki,A Strinić

doi:10.1038/s41535-021-00417-3

Abstract

Magnetoelectric phenomena are intimately linked to relativistic effects and also require the material to break spatial inversion symmetry and time-reversal invariance. Magnetoelectric coupling can substantially affect light–matter interaction and lead to non-reciprocal light propagation. Here, we confirm on a fully experimental basis, without invoking either symmetry-based or material-specific assumptions, that the optical magnetoelectric effect in materials with non-parallel magnetization (M) and electric polarization (P) generates a trilinear term in the refractive index, δn ∝ k ⋅ (P × M), where k is the propagation vector of light. Its sharp magnetoelectric resonances in the terahertz regime, which are simultaneously electric and magnetic dipole active excitations, make Co2Mo3O8 an ideal compound to demonstrate this fundamental relation via independent variation of M, P, and k. Remarkably, the material shows almost perfect one-way transparency in moderate magnetic fields for one of these magnetoelectric resonances.

Highlights

The intense research on magnetoelectric and multiferroic compounds in recent years[1–5] has revealed a plethora of novel optical phenomena specific to these materials[2,6–37]
In terms of light intensity, it is manifested in the so-called directional dichroism[39,40], when the magnitude of light absorption is different for the two beams with opposite (±k) propagation vectors
We demonstrate that the tripleproduct form of the optical magnetoelectric effect holds when freely propagating electromagnetic waves in the THz regime are brought into interaction with a multiferroic material

Summary

Introduction

The intense research on magnetoelectric and multiferroic compounds in recent years[1–5] has revealed a plethora of novel optical phenomena specific to these materials[2,6–37]. We chose a type-I multiferroic, the polar easy-axis antiferromagnet Co2Mo3O844, as a benchmark material to systematically test the triple-product form, k ⋅ (P × M), of the directional optical anisotropy. Similar to the cases of the antiferromagnetic Fe2Mo3O824, and ferrimagnetic Zn-doped Fe2Mo3O825,56 and Mn2Mo3O857, in the low-energy range (

Results

Conclusion