Influence of low-energy magnons on magnon Hanle experiments in easy-plane antiferromagnets

TL;DR

This study investigates how low-energy magnons influence magnon Hanle experiments in easy-plane antiferromagnets, revealing distinct behaviors in films of different thicknesses and highlighting the role of finite-spin low-energy magnons.

Contribution

The paper extends the magnonic spin transport model by explicitly including finite-spin low-energy magnons and experimentally demonstrates their impact on the magnon Hanle effect.

Findings

Observation of magnon Hanle signals in both thin and thick hematite films.

Differences in the magnonic spin signals between 15 nm and 100 nm films.

Identification of an offset signal in thicker films attributed to low-energy magnons.

Abstract

Antiferromagnetic materials host pairs of spin-up and spin-down magnons which can be described in terms of a magnonic pseudospin. The close analogy between this magnonic pseudospin systems and that of electronic charge carriers led to the prediction of fascinating phenomena in antiferromagnets. Recently, the associated dynamics of antiferromagnetic pseudospin has been experimentally demonstrated and, in particular, the first observation of the magnon Hanle effect has been reported. We here expand the magnonic spin transport description by explicitly taking into account contributions of finite-spin low-energy magnons. In our experiments we realize the spin injection and detection process by two Platinum strips and investigate the influence of the Pt-strips on the generation and diffusive transport of magnons in films of the antiferromagnetic insulator hematite. For both a 15 nm and a 100 nm thick film, we find a distinct signal caused by the magnon Hanle effect. However, the magnonic spin signal exhibits clear differences in both films. In contrast to the thin film, for the thicker one, we observe an oscillating behavior in the high magnetic field range as well as an additional offset signal in the low magnetic field regime. We attribute this offset signal to the presence of finite-spin low-energy magnons.