Correlations, spin dynamics, defects: the highly-frustrated Kagom\'{e} bilayer

TL;DR

This study investigates highly-frustrated Kagomé bilayer magnets, revealing a spin-liquid ground state with short-range correlations, persistent low-temperature spin fluctuations, and defect-induced paramagnetic contributions, supporting the Resonating Valence Bond theory.

Contribution

The paper provides experimental evidence of a spin-liquid state in Kagomé bilayer compounds through multiple magnetic measurements, highlighting the role of defects and low-temperature dynamics.

Findings

Short-range spin correlations persist at low temperatures.

No long-range magnetic order observed down to 30 mK.

Presence of low-temperature spin fluctuations indicating a dynamical ground state.

Abstract

The SrCr$\_{9p}$Ga$\_{12-9p}$O$\_{19}$ and Ba$\_{2}$Sn$\_{2}$ZnGa$\_{10-7p}$Cr$\_{7p}$O$\_{22}$ compounds are two highly-frustrated magnets possessing a quasi-two-dimensional Kagom\'{e} bilayer of spin 3/2 chromium ions with antiferromagnetic interactions. Their magnetic susceptibility was measured by local Nuclear Magnetic Resonance and non-local (SQUID) techniques, and their low-temperature spin dynamics by Muon Spin Resonance. Consistent with the theoretical picture drawn for geometrically frustrated systems, the Kagom\'{e} bilayer is shown here to exhibit: (i) short range spin-spin correlations down to a temperature much lower than the Curie-Weiss temperature, no conventional long-range transition occurring; (ii) a Curie contribution to the susceptibility from paramagnetic defects generated by spin vacancies; (iii) low-temperature spin fluctuations, at least down to 30 mK, which are a trademark of a dynamical ground state. These properties point to a spin-liquid ground state, possibly built on Resonating Valence Bonds with unconfined spinons as the magnetic excitations.