Chiral exchange drag and chirality oscillations in synthetic antiferromagnets

Abstract

Long-range interactions between quasiparticles give rise to a ‘drag’ that affects the fundamental properties of many systems in condensed matter physics1,2,3,4,5,6,7,8,9,10,11. Drag typically involves the exchange of linear momentum between quasiparticles and strongly influences their transport properties. Here, we describe a kind of drag that involves the exchange of angular momentum between two current-driven magnetic domain walls. The motions of the domain walls are correlated and determined by the strength of the drag. When the drag is below a threshold value, the domain walls move together at a constant intermediate velocity with a steady leakage of angular momentum from the faster to the slower wall. However, we find that when the drag exceeds a threshold value, a different dynamic can take place in which the faster domain wall’s magnetization oscillates synchronously with a precessional motion of the slower domain wall’s magnetization, and angular momentum is continuously transferred between them. Our findings demonstrate a method for delivering spin angular momentum remotely to magnetic entities that otherwise could not be manipulated directly by current, for example, by coupling domain walls or other non-collinear spin textures in metallic and insulating media.

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Fig. 1: Magnetic properties of SAF films and current-driven domain motion in SAF wires.
Fig. 2: Micromagnetic simulations of chiral exchange drag dynamics in SAF wire.
Fig. 3: Analytical model simulations of chiral exchange drag dynamics in a SAF wire.
Fig. 4: CED dynamics as a function of J, \({{H}}_{{L}}^{{{DM}}}\), Jex and \(\frac{{{{M}}_{{R}}}}{{{{M}}_{{S}}}}\).

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank the Army Research Office (contract no. W911NF-13-1-0107) for their partial support of this work.

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Contributions

S.-H.Y. and S.S.P.P. conceived and designed these studies. S.-H.Y. grew the films and patterned devices. C.G. measured devices, analysed the experimental data and carried out the micromagnetic simulations. S.-H.Y. interpreted the results and developed the model. S.-H.Y. and S.S.P.P. wrote the manuscript. All authors discussed the results and made contributions to the manuscript.

Corresponding authors

Correspondence to See-Hun Yang or Stuart S. P. Parkin.

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Supplementary information

Supplementary Information

Additional theoretical derivations, Supplementary References 1–4 and Supplementary Figures 1–8.

Supplementary Video 1

Analytical model calculation of time-resolved current-driven DW motion. Hx= 2 kOe.

Supplementary Video 2

Analytical model calculation of time-resolved current-driven DW motion. Hx = −1.05 kOe.

Supplementary Video 3

Analytical model calculation of time-resolved current-driven DW motion. Hx = −1.1 kOe.

Supplementary Video 4

Analytical model calculation of time-resolved current-driven DW motion. Hx = −2 kOe.

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Yang, SH., Garg, C. & Parkin, S.S.P. Chiral exchange drag and chirality oscillations in synthetic antiferromagnets. Nat. Phys. 15, 543–548 (2019). https://doi.org/10.1038/s41567-019-0438-3

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