Toward an Ideal S = 1/2 Kagome Antiferromagnet and Quantum Spin Liquid Candidate through Selective Mg 2+ Doping of Averievite

Abstract Quantum spin liquids (QSLs) are exotic states of matter where geometric frustration and quantum fluctuations suppress conventional magnetic order. S = 1/2 kagome antiferromagnets (KAFMs) are an ideal platform for realizing such behavior, and several mineral-inspired Cu2+-based kagome systems have emerged as promising candidates. Among these, Averievite (Cu5V2O10CsCl) offers a structurally distinct route to frustrated magnetism through its copper oxovanadate framework, which hosts alternating kagome and honeycomb layers. Prior studies have shown that targeted Zn2+ substitution on the honeycomb CuH site can suppress magnetic order and promote QSL-like behavior. Here we investigate Mg2+ substitution in the Averievite family, motivated by the geometric flexibility and favorable scattering contrast of Mg2+ relative to Zn2+, the previously explored diamagnetic dopant. Herein we present the novel MgxCu5–xV2O10CsCl (x = 0, 0.5, 1, 2) family, utilizing X-ray diffraction, single-crystal electron diffraction, and SQUID magnetometry to obtain precise structural parameters, including site occupancies, antisite disorder, and local coordination information, and to correlate these with the varied magnetic behavior. Increasing Mg2+ content leads to a pronounced suppression of both the structural and long-range magnetic ordering, alongside an increased mean field antiferromagnetic interaction, signaling enhanced magnetic frustration. Crucially, electron diffraction data is indicative of less than 1% Mg2+ antisite disorder onto the kagome lattice in the Mg2 compound. This contrasts with Zn-based analogues, preserving the integrity of the S = 1/2 kagome network. At x = 2, neither long-range order nor spin freezing is observed down to 2K, giving a new S = 1/2 KAFM with early hallmarks of QSL behavior and establishing Mg-doped Averievite as a clean and highly tunable platform for exploring QSL ground states.