Ordering in weakly coupled random singlet spin chains

TL;DR

This paper investigates how bond randomness affects magnetic ordering in weakly coupled S=1/2 antiferromagnetic spin chains, revealing significant effects on ordering temperature and magnetization, and discusses the potential universality of ordered moment distribution.

Contribution

It provides experimental evidence of disorder effects on magnetic order in random singlet spin chains and questions existing mean field theory predictions.

Findings

Disorder strongly affects the ordering temperature TN.

Saturation magnetization m0 is significantly reduced by randomness.

Behavior suggests a universal distribution of ordered moments.

Abstract

The influence of bond randomness on long range magnetic ordering in the weakly coupled S = 1/2 antiferromagnetic spin chain materials Cu(py)2(Cl1-xBrx)2 is studied by muon spin rotation and bulk measurements. Disorder is found to have a strong effect on the ordering temperature TN, and an even stronger one on the saturation magnetization m0, but considerably more so in the effectively lower-dimensional Br-rich materials. The observed behavior is attributed to Random Singlet ground states of individual spin chains, but remains in contradiction with chain mean field theory predictions. In this context, we discuss the possibility of a universal distribution of ordered moments in the weakly coupled Random Singlet chains model.