Inhomogeneous ordering in weakly coupled Heisenberg $S=1/2$ chains with random bonds

TL;DR

This study investigates how weak disorder affects magnetic ordering in quasi-one-dimensional Heisenberg S=1/2 chains, revealing inhomogeneous order and reduced moments driven by infinite randomness fixed points.

Contribution

It provides experimental evidence of inhomogeneous magnetic order and reduced moments in disordered Heisenberg chains, interpreted through the infinite randomness fixed point framework.

Findings

Reduced saturation ordered moments in disordered samples

Highly inhomogeneous magnetic order observed

Order persists despite weak disorder

Abstract

Long range magnetic ordering in the quasi-one-dimensional random-bond antiferromagnet BaCu$_2$(Si$_{1-x}$Ge$_{x}$)$_2$O$_7$ is studied in $\mu$SR experiments as a function of disorder strength. Compared to the disorder-free parent materials, the saturation ordered moment is found to be considerably reduced. Moreover, even in weakly disordered species, the magnetically ordered state is shown to be highly inhomogeneous. The results are interpreted in terms of weakly coupled random spin chains, governed by the ``infinite randomness`` fixed point.