Random magnetism in the frustrated triangular spin ladder KCu ₅V₃O₁₃

We present susceptibility, high-field magnetization, and Raman scattering measurements of the frustrated spin system KCu₅V₃O ₁₃, consisting of ladders of Cu²⁺ tetrahedra. The magnetic susceptibility shows a sub-Curie power-law behavior χ(T) ∼ T ^-αs with α_s=0.43 and 0.60 for low temperatures 8 K < T < 20 K and intermediate temperatures 20 K < T < 140 K, respectively. The magnetization at 8 K also follows a power law M ∝ H ^1-αm with α_m=0.45, indicating that the magnetic behavior is dominated by random interactions. Raman scattering measurements show substantial local lattice distortions arising from a change of covalency as a function of temperature. Our study suggests that a random spin singlet state can be realized in low-dimensional frustrated spin systems induced by temperature-dependent lattice distortions.