Pressure Effect on Haldane Gap System

Abstract The [Ni(dmpn) 2 N 3 ]ClO 4 (dmpn=2,2-dimethyl-1,3-propylenediamine) is a Haldane gap compound with Eg=21.6 K and J=−70.6 K. The pressure effect on the magnetic susceptibilities has revealed that with increase of the pressure the absolute J values increase. This is due to the increase of the orbital overlapping between the Ni 2+ ions and the N atoms of bridging azido-ligands.