Anisotropic Spin Freezing in theS=1/2Zigzag Chain CompoundSrCuO2

Abstract

We characterize an unusual magnetic phase in orthorhombic ${\mathrm{SrCuO}}_2$ using neutron scattering. ${\mathrm{SrCuO}}_2$ contains zigzag spin chains formed by pairs of linear $S=1\mathrm{}/2$ chains ( $J=180\mathrm{}$ meV) coupled through a frustrated interaction ( $|J^{\prime }|\lesssim 0.1J$). For $T<\mathrm{}{T}_{c1\mathrm{}}=5.0\mathrm{}\left(4\right)$ K, an elastic peak develops in a gapless spectrum indicating spin freezing on a time scale $\delta t>\mathrm{}2\mathrm{}̇{10}^{-10\mathrm{}}$ s. While the frozen state has long range order along chains ( ${\xi }_c>200c$) and a substantial correlation length, ${\xi }_a=60\mathrm{}\left(25\right)a$, perpendicular to zigzag planes, the correlation length is only ${\xi }_b=2.2\mathrm{}\left(3\right)b$ in the direction of frustrated interactions. We argue that slow dynamics of stripelike cooperative magnetic defects yield this anisotropic frozen state.