Comment on "Unconventional Magnetism in a Nitrogen-Containing Analog of   Cupric Oxide"
  In a recent Letter [PRL, 107, 047208 (2011)], Zorko et al. report on an "unexpected inhomogeneous magnetism" related to "a peculiar fragility" of the resonating-valence-bond (RVB) electronic state in the spin-1/2 quantum magnet CuNCN. Here, we show that: i) the spin model of the anisotropic triangular lattice (ATL), as proposed by Zorko et al., does not apply to CuNCN; ii) this model does not support the proclaimed RVB ground state in the relevant parameter range; iii) the magnetic state of CuNCN is not necessarily inhomogeneous. 
Alexander A. Tsirlin and Helge Rosner
cond-mat.mtrl-sci cond-mat.str-el