Switching of the gapped singlet spin-liquid state to an antiferromagnetically ordered state in Sr(Cu1−xZnx)2O3

Abstract

Magnetic susceptibility and specific heat were measured for a Zn-substituted spin-1/2 Heisenberg two-leg ladder compound Sr(${\mathrm{Cu}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Zn}}_{\mathrm{x}}$ ${)}_2$ ${\mathrm{O}}_3$ (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 an antiferromagnetic ordering was observed both in the magnetic susceptibility and the specific heat at low temperature even at only 1% of Zn. The Néel temperature showed a systematic Zn concentration dependence with a broad maximum at around 4% substitution (${\mathrm{T}}_{\mathrm{Nmax}}$∼8 K). A finite amount of a T-linear term with a coefficient of γ∼3.5 mJ/${\mathrm{K}}^2$ was observed in the specific heat above ${\mathrm{T}}_{\mathrm{N}}$ for x=0.02 and 0.04, suggesting that the spin excitation in the substituted compound becomes gapless.