Correlation between unconventional spin Hall effect and crystal structure in the noncollinear antiferromagnet Mn3Sn

Noncollinear antiferromagnets have emerged as promising platforms for next-generation spintronic devices due to their unique spin textures and unconventional spin-polarized currents. However, the limited understanding of factors governing the out-of-plane spin polarization efficiency (${\ensuremath{\xi}}_{\mathrm{z}}$) in materials such as $\mathrm{M}{\mathrm{n}}_{3}\mathrm{Sn}$ hinders their practical application. Here, we demonstrate a strain-engineering strategy to significantly enhance ${\ensuremath{\xi}}_{\mathrm{z}}$ by tailoring the lattice constant $c$ of $\mathrm{M}{\mathrm{n}}_{3}\mathrm{Sn}$ thin films. Through controlled annealing processes, we induce tunable crystalline strain in $\mathrm{M}{\mathrm{n}}_{3}\mathrm{Sn}$ and systematically investigate its impact on spin-to-charge conversion via angle-resolved spin-torque ferromagnetic resonance measurements. Remarkably, the unconventional dampinglike torque efficiency increases by over an order of magnitude when the lattice constant $c$ approaches its equilibrium value, attributed to strain-modulated chiral spin configurations. First-principles calculations corroborate the critical role of lattice strain in amplifying anisotropic spin textures and spin-orbit coupling. This work not only elucidates the structural origin of spin polarization anisotropy in noncollinear antiferromagnets but also establishes a scalable route for designing high-efficiency spin sources compatible with semiconductor integration. The findings advance the development of low-power, all-electric spintronic devices based on strain-engineered antiferromagnetic heterostructures.