Impurity effects on a 2-leg spin ladder compound SrCu₂O₃

Measurements of magnetic susceptibility, specific heat and inelastic neutron scattering were performed on a Zn-substituted spin-1/2 Heisenberg 2-leg ladder compound Sr(Cu_1-xZn_x)₂O₃ (x ≤ 0.08) to investigate nonmagnetic impurity effects on the quantum spin system with a large spin gap of about ∼ 400 K. A clear anomaly attributed to the onset of antiferromagnetic ordering was observed both in the magnetic susceptibility and specific heat data even at only 1 % of Zn. The Néel temperature showed a systematic Zn-concentration dependence with a broad maximum at around 4 % substitution (T_Nmax ∼ 8K). A finite amount of T-linear term with a coefficient of γ ∼ 3.5 mJ/K² was observed in the specific heat above T_N for x = 0.02 and 0.04, suggesting the existence of a finite density of states at E = 0 in the spin excitation spectrum as supported by the inelastic neutron scattering measurement.