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Efficient spin excitation via ultrafast damping-like torques in antiferromagnets

December 1, 2020

Damping effects form the core of many emerging concepts for high-speed spintronic applications. Important characteristics such as device switching times and magnetic domain-wall velocities depend critically on the damping rate. While the implications of spin damping for relaxation processes are intensively studied, damping effects during impulsive spin excitations are assumed to be negligible because of the shortness of the excitation process. Herein we show that, unlike in ferromagnets, ultrafast damping plays a crucial role in antiferromagnets because of their strongly elliptical spin precession. In time-resolved measurements, we find that ultrafast damping results in an immediate spin canting along the short precession axis. The interplay between antiferromagnetic exchange and magnetic anisotropy amplifies this canting by several orders of magnitude towards large-amplitude modulations of the antiferromagnetic order parameter. This leverage effect discloses a highly efficient route towards the ultrafast manipulation of magnetism in antiferromagnetic spintronics.

a Projection of the YMnO3 crystal structure onto the basal plane. Mn3+ ions (violet) in grey and white areas are located in planes at z = 0 and z = c/2, respectively. The three sublattice magnetisations Mi point along equivalent x axes xi as indicated in the coordinate system. Note that spins in HoMnO3 point along equivalent y axes for TSR < T < TN (Supplementary Fig. 1). b Schematic of the setup. The pump and probe pulses are circularly and linearly polarised, respectively. P polariser, λ/4 quarter-wave plate, WP Wollaston prism, BPD balanced photodiode. c Visualisation of optical Z-mode excitation with field-like and damping-like torques ΤFL and TDL exerted by the effective field HIFE of the IFE on the magnetisation Mi ‖ x̂i (x̂i denotes the unit vector in the direction xi). Black lines illustrate the ensuing strongly elliptical spin precession. Dashed ellipses show the expected trajectory without spin excitation via TDL. Precession amplitudes are significantly reduced.
Reference: Tzschaschel, C., Satoh, T., and Fiebig, M. (2020). Efficient spin excitation via ultrafast damping-like torques in antiferromagnets. Nature Commun 11, 6142. (10.1038/s41467-020-19749-y)

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