Correlations, spin dynamics, defects: the highly-frustrated Kagom\'e bilayer
Abstract
The SrCr\9pGa\12-9pO\19 and Ba\2Sn\2ZnGa\10-7pCr\7pO\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.
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