Spin density distribution in a partially magnetized organic quantum   magnet
  Polarized neutron diffraction experiments on an organic magnetic material reveal a highly skewed distribution of spin density within the magnetic molecular unit. The very large magnitude of the observed effect is due to quantum spin fluctuations. The data are in quantitative agreement with direct diagonalization results for a model spin Hamiltonian, and provide insight on the actual microscopic origin of the relevant exchange interactions. 
A. Zheludev, V. O. Garlea, S. Nishihara, Y. Hosokoshi, A. Cousson, A.   Gukasov and K. Inoue