| We review very high field NMR results on quantum spin systems, which where recently obtained at the Grenoble High Magnetic field Laboratory. In the "Shastry-Sutherland" compound, SrCu2(BO3)2, we proved that the spin superlattice formed in the 1/8 plateau does not melt but survives in the intermediate phase between the 1/8 and the 1/4 plateau. A new phase was observed just above the 1/8 plateau, which might correspond to a sort of "supersolid-like" phase, in which the superlattice of longitudinal polarization coexists with a new long range order of the transverse staggered polarization [M. Takigawa et al., cond-mat/0710.5216]. In the "Han purple" compound, BaCuSi2O6, we found that the average boson density in the BEC phase is strongly modulated along the c axis in a ratio of the order of 1:5 for every second plane, whereas its local value is IC modulated within each plane. We thus proposed that the pertinent driving mechanism for decoupling of 2D planes is not only the frustration, but also the difference in the intradimer coupling for the two planes, leading to nearly zero boson density in every second plane [S. Krämer et al., Phys. Rev. B 76, 100406(R) (2007)]. In the azurite, Cu3(CO3)2(OH)2, which is the first recognized model system for a (frustrated) diamond spin chain, we characterized the local spin polarization over the whole 1/3 plateau. Above this plateau, i.e., above 31 T, the system evolves into the fully polarized state through a new, unknown incommensurate phase [S. Krämer et al., unpublished]. |
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