Ground State of the Kagomé-Like S = 1 / 2 Antiferromagnet Volborthite C$u_3$ $V_2$ $O_7$ (OH$)_2$ · 2$H_2$O

F. Bert (1) , D. Bono (1) , P. Mendels (1) , F. Ladieu (2, 3) , F. Duc (4) , J.-C. Trombe (4) , P. Millet (4)

1 LPS - Laboratoire de Physique des Solides
2 SPHYNX - Systèmes Physiques Hors-équilibre, hYdrodynamique, éNergie et compleXes
3 SPEC - UMR3680 - Service de physique de l'état condensé
4 CEMES - Centre d'élaboration de matériaux et d'études structurales

The volborthite compound is one of the very few realizations of S=1/2 quantum spins on a highly frustrated kagomé-like lattice. Low-{\it T} SQUID measurements reveal a broad magnetic transition below 2K which is further confirmed by a peak in the $^{51}$V nuclear spin relaxation rate (1/$T_1$) at 1.4 K \pm 0.2 K. Through $^{51}$V NMR, the ground state (GS) appears to be a mixture of different spin configurations, among which 20% corresponds to a well defined short-range order, possibly of the $\sqrt 3$ x $\sqrt 3$ type. While the freezing involves all the C$u_{2,+}$ spins, only 40% of the copper moment is actually frozen which suggests that quantum fluctuations strongly renormalize the GS.

Domaines: Physique [physics]

F. Bert, D. Bono, P. Mendels, F. Ladieu, F. Duc, et al.. Ground State of the Kagomé-Like S = 1 / 2 Antiferromagnet Volborthite C$u_3$ $V_2$ $O_7$ (OH$)_2$ · 2$H_2$O. Physical Review Letters, 2005, 95, pp.087203. ⟨10.1103/PhysRevLett.95.087203⟩. ⟨cea-01395314⟩