Anisotropic Kitaev spin glass in Li2RuxIr1−xO3

Abstract Kitaev iridates are an important class of spin-orbit-entangled quantum materials, where bond-directional exchange generates strong magnetic frustration and unconventional correlated states. The α , β , γ − Li 2 IrO 3 family exhibit fragile and highly anisotropic magnetic behavior, including incommensurate counter-rotating order, strong field sensitivity, and pressure-driven electronic reconstruction. Understanding how chemical substitution perturbs these competing interactions provides a route toward probing the underlying frustrated magnetic state. Here, we study single crystals of β − Li 2 Ru x Ir 1− x O 3 with dilute Ru substitution, x ≲ 10%. Through magnetometry, resonant elastic X-ray scattering, a c -heat capacity, and muon spin relaxation/rotation, we show that weak magnetic disorder suppresses the incommensurate antiferromagnetic ground state. Instead, the system evolves into a bulk spin glass characterized by slow relaxation and frozen, local magnetic fields. Despite the loss of long-range order, the glassy state retains substantial directional anisotropy, evidenced by enhanced b -axis magnetic susceptibility and direction-dependent thermoremanent relaxation. Structural probes further indicate that Ru substitution leaves the hyperhoneycomb lattice largely undistorted while disrupting magnetic coherence, suggesting that disorder freezes spins within a still-active bond-directional exchange environment. In this picture, dilute Ru substitution provides a controlled pathway into an anisotropic Kitaev spin glass regime that preserves essential fingerprints of the underlying Kitaev exchange network.