Room-temperature anisotropic in-plane spin dynamics in graphene induced by PdSe₂ proximity

van der Waals heterostructures provide a versatile platform for tailoring electrical, magnetic, optical and spin transport properties via proximity effects. Hexagonal transition metal dichalcogenides induce valley Zeeman spin-orbit coupling in graphene, creating spin lifetime anisotropy between in-plane and out-of-plane spin orientations. However, in-plane spin lifetimes remain isotropic due to the inherent heterostructure's three-fold symmetry. Here we demonstrate that pentagonal PdSe₂, with its unique in-plane anisotropy, induces anisotropic gate-tunable spin-orbit coupling in graphene. This enables a tenfold modulation of spin lifetimes at room temperature, depending on the in-plane spin orientation. Moreover, the directional dependence of the spin lifetimes, along the three spatial directions, reveals a persistent in-plane spin texture component that governs the spin dynamics. These findings advance our understanding of spin physics in van der Waals heterostructures and pave the way for designing topological phases in graphene-based heterostructures in the strong spin-orbit coupling regime.