Nh4Ni(mnt)2H2O— a low-dimensional organic ferromagnet

We report on the magnetic and transport properties of the organic salt NH 4 Ni(mnt) 2 H 2 O where (mnt) is the maleonitrile dithiolate ligand. This material is antiferromagnetic down to 100K, below which there is a transition to a paramagnetic state with ferromagnetic exchange. This is accompanied by an increase in resistivity by a factor of two which we consider indicative of a structural phase transition. Long range ferromagnetic order is seen below 4.9K.