Физика Низких Температур: Том 31, Выпуск 8-9 (Август 2005), c. 929-951    ( к оглавлению , назад )

Correlations, spin dynamics, defects: the highly-frustrated Kagomé bilayer

David Bono*, Laurent Limot**, and Philippe Mendels

Laboratoire de Physique des Solides, UMR 8502, Université Paris-Sud, 91405 Orsay, France
E-mail: mendels@lps.u-psud.fr

Gaston Collin

Laboratoire Léon Brillouin, CE Saclay, CEA-CNRS, 91191 Gif-sur-Yvette, France

Nicole Blanchard

Laboratoire de Physique des Solides, UMR 8502, Université Paris-Sud, 91405 Orsay, France

Received March 21, 2005

Аннотация

The SrCr9p Ga12-9pO19and Ba2Sn2 ZnGa10-7p Cr7pO22 compounds are two highly-frustrated magnets possessing a quasi-two-dimensional Kagomé bilayer of spin 3/2 chromium ions with antiferromagnetic interactions. Their magnetic susceptibility was measured by local nuclear magnetic resonance and nonlocal (SQUID) techniques, and their low-temperature spin dynamics by muon spin resonance. Consistent with the theoretical picture drawn for geometrically frustrated systems, the Kagomé 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.

PACS:
75.40.Gb - Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Lk - Spin glasses and other random magnets
76.75.+i - Muon spin rotation and relaxation
76.60.-k - Nuclear magnetic resonance and relaxation (see also 33.25.+k Nuclear resonance and relaxation in atomic and molecular physics and 82.56.-b Nuclear magnetic resonance in physical chemistry and chemical physics; for structure determination using magnetic re