Possible coexistence of antiferromagnetic and ferromagnetic spin fluctuations in UTe₂ revealed by ¹²⁵Te NMR under pressure

UTe₂ is a newly discovered heavy-fermion superconductor proposed to be an end member of the U-based ferromagnetic (FM) superconductors. The spin-triplet superconducting state in UTe₂ mediated by FM spin fluctuations has been proposed by muon spin relaxation and nuclear magnetic resonance measurements (NMR). Recently, neutron scattering measurements detected the presence of antiferromagnetic (AFM) spin fluctuations in UTe₂. In this study, we carried out ¹²⁵Te NMR measurements on a single crystal UTe₂ to investigate the evolution of magnetic fluctuations in UTe₂ under pressure. From the temperature dependence of ¹²⁵Te spin-lattice relaxation rates, we propose the possible coexistence of AFM and FM spin fluctuations in the system. In addition, owing to the two different Te sites in the compound, the FM spin fluctuations are considered to exist within the ladders, while the AFM spin fluctuations originate from the inter-ladder magnetic coupling. We point out that although the AFM spin fluctuations exist in the system, the FM spin fluctuations in the ladders may play a more important role in the appearance of the spin-triplet superconducting state of UTe2.