The spin-1/2 of an electron makes it an archetypal two-level system and inspires the description of other two-level systems using an analogous pseudospin. The quantized spin excitations of an ordered antiferromagnet can be viewed as pairs of spin-up and -down magnons and can be characterized by a magnonic pseudospin. The similarity between electronic spin and magnonic pseudospin has triggered the prediction of exciting phenomena like emergent spin-orbit coupling and topological states in antiferromagnetic magnonics. In the last year, first experimental observations of the associated dynamics of antiferromagnetic pseudospin have been reported [1,2]. Based on these findings, we will expand the concept of magnon pseudospin and the description of magnon pseudospin dynamics [3,4] and discuss the influence of dimensionality on the magnon Hanle effect. Additionally, we show our recent experiments demonstrating control of magnon spin transport and pseudospin dynamics in thin films with varying thickness of the antiferromagnetic insulator hematite (α-Fe2O3) utilizing two Pt strips for all-electrical magnon injection and detection [2] . We observe an oscillation in polarity of the magnon spin signal at the detector as a function of the applied magnetic field, which we quantitatively explain in terms of diffusive magnon transport. In particular, we observe a coherent precession of the magnon pseudospin caused by the easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. Moreover, we find peculiar changes in the magnon spin signal for thicker hematite layers. Our results are paramount in unnlocking the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena. Financial support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy - EXC-2111 - 390814868 and project AL2110/2-1, and the Research Council of Norway through its Centers of Excellence funding scheme, project 262633, "QuSpin" is gratefully acknowledged.

Antiferromagnetic Magnon Pseudospin Dynamics and the Magnon Hanle Effect in Hematite Thin Films

The spin-1/2 of an electron makes it an archetypal two-level system and inspires the description of other two-level systems using an analogous pseudospin. The quantized spin excitations of an ordered antiferromagnet are such pairs of spin-up and -down magnons and can be characterized by a magnonic pseudospin. The similarity between electronic spin and magnonic pseudospin has triggered the prediction of exciting phenomena like emergent spin-orbit coupling and topological states in antiferromagnetic magnonics. An experimental observation of the associated dynamics of antiferromagnetic pseudospin, however, has eluded experiments thus far. As a first step we will introduce the concept of magnon pseudospin and the description of magnon pseudospin dynamics, as well as briefly discuss similarities to electron spin transport [1]. In the second part, we show our recent experiments demonstrating control of magnon spin transport and pseudospin dynamics in a 15 nm thin film of the antiferromagnetic insulator hematite (α-Fe2O3) utilizing two Pt strips for all-electrical magnon injection and detection [2] (c.f. Fig. 1 (a)). We observe an oscillation in polarity of the magnon spin signal at the detector as a function of the externally applied magnetic field (see Fig. 1 (b)), which we quantitatively explain in terms of diffusive magnon transport. In particular, we observe a coherent precession of the magnon pseudospin caused by the easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. This observation can be viewed as the magnonic analogue of the electronic Hanle effect and the Datta-Das transistor, unlocking the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena. Financial support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy - EXC-2111 - 390814868 and project AL2110/2-1, and the Research Council of Norway through its Centers of Excellence funding scheme, project 262633, "QuSpin" is gratefully acknowledged.

**References:**

[1] A. Kamra et al., Physical Review B 102, 174445 (2020) [2] T. Wimmer et al., Physical Review Letters 125, 247204 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/ec8627bd4d1b243e84613268af7a73af.jpg)
Fig. 1: (a) Sketch of the device geometry, the electrical wiring, and the coordinate system. The canting of the magnetic sublattices m1 and m2 and the corresponding net moment mnet as well as the Néel order parameter n are illustrated. Upon applying a charge current Iinj to the injector, a spin current Is with spin polarization s is generated via the SHE and injected into the hematite (α-Fe2O3) with thickness t = 15 nm. The emerging antiferromagnetic magnon current is then detected via the inverse SHE induced current at the detector by measuring the electrical voltage drop Veldet. (b) Magnon transport signal Veldet as a function of the external magnetic field magnitude. The signal oscillates between positive and negative values. The qualitative behaviour is very similar to the electronic Hanle effect.

 Observation of Antiferromagnetic Magnon Pseudospin Dynamics and the Magnon Hanle effect

**Session chair:** Romain Lebrun, Unité Mixte de Physique CNRS/Thales



GOP - Antiferromagnetic Spintronics II

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Antiferromagnetic Magnon Pseudospin Dynamics and the Magnon Hanle Effect in Hematite Thin Films

Observation of Antiferromagnetic Magnon Pseudospin Dynamics and the Magnon Hanle effect

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