We report on the generation of ultrafast spin currents through femtosecond laser excitation of epitaxial bilayer thin films comprising $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ (an insulating antiferromagnet) and Pt (a heavy metal). The epitaxial thin films of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ were simultaneously grown in three distinct orientations, namely, R, A, and C planes, employing pulsed laser deposition. By using the R plane $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$, we demonstrate a substantial enhancement of the THz signal, nearly one order of magnitude greater compared to the A and C planes $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}/\mathrm{Pt}$. We perform a detailed investigation into the sample azimuthal and laser polarization dependence of the THz emission. Our investigations establish that the sample azimuthal dependence of THz emission in the $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}/\mathrm{Pt}$ system is linked to the spin domain distribution as well as the crystalline symmetry of the orientation of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$. These results contribute significantly to understanding the ultrafast dynamics of spin currents in antiferromagnets.

Efficient terahertz emission from R-plane <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>α</mml:mi><mml:msub><mml:mtext>-Fe</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi>Pt</mml:mi></mml:mrow></mml:math>

Efficient terahertz emission from R-plane α-Fe2O3/Pt