Pressure effect of an S=1 Haldane compound NDMAZ

We measured the heat capacity of an S = 1. Haldane compound NDMAZ under the pressure to investigate the three-dimensional magnetic ordering due to the anisotropy (D) and/or the interchain interaction. However, the experimenta l result shows that the Haldane gap (Delta) has been enhanced by the pressu re and the magnetic ordering has not been observed. The remarkable increase of intrachain inter action (J) by the pressure will lead to the enhancemen t of Delta. We also discuss about the pressure-induced changes of Delta/\J\ and D/\J\ in this Haldane compound.