A collapse of ferromagnetism in an organic based magnet under pressure.

The metal-organic charge transfer compound NiTCNQ2 has been subjected to pressure where both magnetisation and muon experiments show a suppression of T C with an applied pressure. At 12 kbar, it appears that the sample is paramagnetic and this gives an estimate of the pressure required for switching the transition on/off. The present work also provides some insight into the molecular structure since this behaviour can be explained if the structure is 3D. It is proposed that the TCNQ interactions increase along a stack with increasing pressure which causes spins on the TCNQ to couple into a singlet state with just isolated Ni ions left, which behave paramagnetically