A field-induced exchange flip in a spin linear trimer in a coordination polymer of cobalt and melamine

A coordination polymer of linear trimeric cobalt and melamine has been synthesized. The magnetic isotherms of violet coloured crystals as long as 400 μm show a field-induced transition in an external field of about 2 T at temperatures below 2 K. It is addressed that by assuming the coexistent positive and negative exchange between the nearest-neighbour spins in the linear trimer, this metamagnetic transition can be understood as a transition from antiferromagnetic to ferromagnetic exchange within each trimeric spin cluster without considering long-range magnetic ordering. Although weak inter-cluster or inter-chain exchange to yield a long-range magnetic order is not excluded as another possible and often attributed origin of metamagnetism in low-dimensional spin systems, the present study demonstrates the significance of the exchange flip within each cluster in clustered spin networks. This paves the way towards the realization of stable, yet switchable states of a spin trimer in the realm of coordination chemistry.