All electrical magnon transport experiments in magnetically ordered insulators

Matthias Althammer, Walther-Meißner-Institut

Pure spin currents, i.e. the flow of angular momentum without an accompanying charge current represents a new paradigm in the field of spintronics. Most importantly, pure spin currents can be transported by fermions, i.e. by electrons, in electrical conductors as well as by bosons, i.e. by magnons, the quantized spin excitations in magnetically ordered systems. Interestingly, heterostructures consisting of spin-orbit coupled metals with magnetically ordered insulators allow to investigate pure spin current transport in both regimes and their interconversion at the interface. This approach enables an all electrical injection and detection scheme to study magnon transport phenomena in magnetically ordered insulators [1]. I will present recent results focusing on ferrimagnetic and antiferromagnetic insulators. First, I will present spin conductance measurements in yttrium iron garnet thin films. Here, I will highlight how charge currents can control the magnon spin conductance realizing a compensation of magnon damping via spin-orbit torques [2,3]. In the second part, I will focus on magnon spin transport in antiferromagnetic insulators. The quantized spin excitations of an ordered antiferromagnet with opposite chirality represent pairs of spin-up and -down magnons and this two-level nature can be characterized by a magnonic pseudospin. In the last years, first descriptions and observations of the associated dynamics of antiferromagnetic pseudospin have been reported [1,2,3,4]. I will introduce these magnon pseudospin dynamics and describe how they lead to the manifestation of the magnon Hanle effect in hematite thin films.

[1] M. Althammer, Phys. Stat. Sol. RRL 15, 2100130 (2021)
[2] T. Wimmer et al., Phys. Rev. Lett. 123, 257201 (2019)
[3] J. Gückelhorn et al., Phys. Rev. B 104, L140404 (2021)
[4] T. Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)
[5] A. Kamra et al., Phys. Rev. B 102, 174445 (2020)
[6] J. Gückelhorn et al., Phys. Rev. B 105, 094440 (2022)
[7] J. Gückelhorn et al., arXiv:2209.09040 (accepted in PRL 2023)

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