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decay for high temperatures — see Fig. 12. While spins are perfectly collinear at low temperatures [Fig. 14(a)], the z axis is now singled out by magnetic field, and Q 3 z $^{2}$− r 2 contributes to P ( r ) . 

This means that there is no symmetry breaking associated with the smooth rise in collinearity for T ∗ ≈ b , which should be regarded as a crossover rather than a phase transition. Sin- 

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gular features are similarly absent from the heat capacity, shown in Fig. 14(b). This smooth change is also seen in the rescaled plot of the spin correlations shown in Fig. 13. The crossover from the low– T power–law behavior to the high– T exponential decay is much more smooth compared to the case for the nematic transition at h = 0 in Fig. 8. This suggests a smooth growth of the characteristic length scale ξ$_{c}$ ∼ 1 $_{/}$√$_{T}$ at T ∼ T ∗ ≈ b . We therefore conclude that the magnetiza- tion plateau is a true spin–liquid state, continuously conn ected with the high– T paramagnet. We refer to this as the plateau liquid below. 

