Spin Configuration in the 1/3 Magnetization Plateau of Azurite Determined by NMR

F. Aimo (1) , S. Kramer (1) , M. Klanjsek (1, 2) , M. Horvatic (1) , C. Berthier (1) , H. Kikuchi (3)

1 LCMI-GHMFL - Laboratoire des champs magnétiques intenses
2 IJS - Jozef Stefan Institute [Ljubljana]
3 Department of Applied Physics, University of Fukui

High magnetic field $^{63,65}$Cu NMR spectra were used to determine the local spin polarization in the 1/3 magnetization plateau of azurite, Cu$_3$(CO$_3$)$_2$(OH)$_2$, which is a model system for the distorted diamond antiferromagnetic spin-1/2 chain. The spin part of the hyperfine field of the Cu2 (dimer) sites is found to be field independent, negative and strongly anisotropic, corresponding to $\approx$10\,\% of fully polarized spin in a $d$-orbital. This is close to the expected configuration of the ``quantum'' plateau, where a singlet state is stabilized on the dimer. However, the observed non-zero spin polarization points to some triplet admixture, induced by strong asymmetry of the diamond bonds $J_1$ and $J_3$.

Domaines: Electrons fortement corrélés [cond-mat.str-el]

F. Aimo, S. Kramer, M. Klanjsek, M. Horvatic, C. Berthier, et al.. Spin Configuration in the 1/3 Magnetization Plateau of Azurite Determined by NMR. Physical Review Letters, 2009, 102, pp.127205. ⟨10.1103/PhysRevLett.102.127205⟩. ⟨hal-00350473v2⟩