Spin-glass behaviour in the coordination polymer [Co(C3H3N2)2]n

The magnetic behaviour of the coordination polymer Co(C(3)H(3)N(2))(2)](n) has been investigated by magnetization and specific heat measurements. Low-field magnetic susceptibility shows the presence of two maxima at approximately 8 and 4 K (T(f)), which reflect short-range low-dimensional antiferromagnetic behaviour and the existence of a spin-glass-like state, respectively. The latter state was observed by magnetic irreversibility in both the zero-field cooled and field-cooled data, and was also confirmed by specific heat measurements. The magnetic specific heat (C(mag)) shows a lack of any long-range ordered peaks. Instead, a broad maximum near T(f) was observed in the C(mag)(T)/T-curve. Below T(f), the C(mag)(T) data follow the relation: C(mag)(T)/T = gamma + AT. We suggest that the competition of the antiferromagnetic (AF) intra-chain and the ferromagnetic (F) inter-chain interactions in a low-dimensional arrangement of magnetic Co(2+) ions can produce the spin-glass behaviour in the sample. The susceptibility data was analyzed in terms of a spin S = 3/2 Heisenberg linear-chain model with a small exchange energy and is consistent with the presence of both F and AF interactions. The splitting of the crystal field energy levels of the Co(2+) ions causes a Schottky-type specific heat anomaly of around 60 K.