Direct observation of local Mn-Mn distances in the paramagnetic compound   CsMnxMg1-xBr3
  We introduce a novel method for local structure determination with a spatial resolution of the order of 0.01 Angstroem. It can be applied to materials containing clusters of exchange-coupled magnetic atoms. We use neutron spectroscopy to probe the energies of the cluster excitations which are determined by the interatomic coupling strength J. Since for most materials J is related to the interatomic distance R through a linear relation dJ/dR={\alpha} (for dR/R<<1), we can directly derive the local distance R from the observed excitation energies. This is exemplified for the mixed one-dimensional paramagnetic compound CsMnxMg1 xBr3 (x=0.05, 0.10) containing manganese dimers oriented along the hexagonal c-axis. Surprisingly, the resulting Mn-Mn distances R do not vary continuously with increasing internal pressure, but lock in at some discrete values. 
A. Furrer, Th. Str\"assle, J. P. Embs, F. Juranyi, V. Pomjakushin, M.   Schneider and K. W. Kr\"amer
cond-mat.mtrl-sci cond-mat.other