Antiferromagnetic order in weakly coupled random spin chains

Abstract

The ordering of weakly coupled random antiferromagnetic $S=1/2$ chains, as\nrelevant for recent experimentally investigated spin chain materials, is\nconsidered theoretically. The one-dimensional isotropic Heisenberg model with\nrandom exchange interactions is treated numerically on finite chains with the\ndensity-matrix renormalization-group approach as well as with the standard\nrenormalization analysis, both within the mean-field approximation for\ninterchain coupling $J_{\\perp}$. Results for the ordering temperature $T_N$ and\nfor the ordered moment $m_0$ are presented and are both reduced with the\nincreasing disorder agreeing with experimental observations. The most\npronounced effect of the random singlet concept appears to be a very large span\nof local ordered moments, becoming wider with decreasing $J_{\\perp}$,\nconsistent with $\\mu$SR experimental findings.\n