Antiferromagnetic order in weakly coupled random spin chains

TL;DR

This paper investigates how weak interchain coupling and disorder affect antiferromagnetic order in random spin chains, revealing that disorder reduces ordering temperature and moment, and causes a wide distribution of local moments, aligning with experiments.

Contribution

It provides a numerical and analytical study of antiferromagnetic order in disordered spin chains, highlighting the impact of randomness on ordering properties and moment distribution.

Findings

Disorder reduces the Néel temperature and ordered moment.

Random singlet effects lead to a broad distribution of local moments.

Results agree with experimental observations of spin chain materials.

Abstract

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