Disorder-induced spin-cluster magnetism in a doped kagome spin liquid candidate

TL;DR

This study investigates how lattice imperfections and Kitaev interactions influence magnetic behavior in a doped kagome spin liquid candidate, revealing disorder-induced spin-cluster magnetism and unusual ferromagnetic canting.

Contribution

It introduces theoretical models explaining the emergence of ferromagnetic canting and short-range order due to disorder and Kitaev interactions in doped kagome systems.

Findings

Observation of in-plane ferromagnetic canting in doped kagome samples

Identification of Kitaev interactions arising from Dzyaloshinskii-Moriya exchanges

Disorder stabilizes short-range magnetic regimes

Abstract

The search for new quantum spin liquid materials relies on systems with strong frustration such as spins on an ideal kagome lattice. However, lattice imperfections can have substantial effects which are as yet not well understood. In recent work, the two-dimensional kagome system YCu$_3$(OH)$_6$[(Cl$_x$Br$_{(1-x)}$)$_{3-y}$(OH)$_y$] has emerged as a leading candidate hosting a Dirac spin liquid which appears to survive at least for x<0.4, associated with alternating-bond hexagon (ABH) disorder. Here in magnetic samples with x=0.58, y=0.1 we report unusual in-plane ferromagnetic canting (FM) of the in-plane antiferromagnet (AFM), with an unusually wide regime of short-ranged order, and propose theoretical models to explain this behavior. First, we show that Kitaev type exchanges naturally arise on the kagome lattice to second order in the known Dzyaloshinskii-Moriya exchanges, and that these interactions can produce the unusual in-plane FM canting from antichiral AFM. Second, we propose a phenomenological model of weakly-FM-canted spin clusters to describe the short-ranged regime and analyze quantum fluctuations in an ABH toy model to show how ABH disorder can stabilize this regime. The combination of experimental observation and theory suggests that kagome-Kitaev interactions and ABH disorder are necessary for describing the magnetic fluctuations in this family of materials, with potential implications for the proposed proximate spin liquid phase.