Recent progress in revealing the superconducting state (SC) symmetry in Sr₂RuO₄ is also marked by unanswered questions. For example, the field-dependent drop in oxygen-17 Knight shift points to an even parity state [1], while research into the relationship of Time-Reversal Symmetry Breaking to the superconducting state is ongoing [2-4]. Since correlations underly the emergent unconventional SC state, both ferromagnetic and antiferromagnetic (AF) fluctuations have been considered in this context [5]. To further elucidate the AF state discovered with m⁺SR measurements [2], we studied oxygen-17 NMR spectroscopy and relaxation under conditions of similarly high uniaxial stress applied // a-axis. The AF phase was found only over a narrow range of applied stress and the relaxation is consistent with Fermi liquid behavior outside it and close to the phase boundary. The spectroscopic changes observed for the 3 inequivalent 17O sites combined with a variable field angle constrain the wavevector Q and the sublattice polarization. Observations indicate an AF state distinct from the fluctuations seen in inelastic neutron scattering experiments under ambient conditions. The role of the reconstructed Fermi surface appearing at high strain is discussed.

[1] A. Chronister, et al., Proc. Natl. Acad. Sci. U.S.A. 118 e2025313118 (2021)

[2] V. Grinenko, et al., Nat. Phys. 17, 748-754 (2021).

[3] Y.-S. Li, et al., Nature 607, 276-280 (2022).

[4] Y. Li, et al., arXiv:2512.24585.

[5] K. Jenni, et al., Phys. Rev. B 103, 104511 (2021).