Regensburg 2019 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 26: Spin dynamics and transport

MA 26.7: Vortrag

Mittwoch, 3. April 2019, 11:00–11:15, H37

Tracking the order parameter motion during a coherent antiferromagnetic spin precession — •Christian Tzschaschel¹, Takuya Satoh², and Manfred Fiebig¹ — ¹Department of Materials, ETH Zurich, Switzerland — ²Department of Physics, Kyushu University, Japan

Recently, antiferromagnets attract increasing attention for spintronics applications. The high frequency of antiferromagnetic (AFM) resonances suggests the possibility to coherently control AFM order on picosecond time scales. AFM spin dynamics, however, are often obscured by the relative inaccessibility of the AFM order parameter. Here, we directly reveal the dynamics of the AFM order using time-resolved optical second-harmonic generation (SHG). Exploiting the inverse Faraday effect, we optically excite a specific magnon mode in hexagonal YMnO₃ and track the ensuing order-parameter dynamics. The coherent Z-mode precession results in a symmetry reduction of the AFM order from 6mm to 3. SHG as a symmetry sensitive technique allows us to separate electron from spin dynamics, which enables a time-resolved quantitative tracking of the AFM order parameter. Specifically, we can estimate the optically induced spin canting angle to be approximately 0.5^∘. In combination with the simultaneously measured Faraday rotation, we obtain access to both the compensated and uncompensated components of the order parameter, which allows us to track its motion during the AFM spin precession. Probing dynamic symmetry reductions constitutes a general approach, which allows tracking AFM spin dynamics also in anharmonic situations, such as spin reorientations.