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

Abstract

The magnetic behaviour of the coordination polymer [Co(C₃H₃N₂)₂]_n has been investigated by magnetization and specific heat measurements. Low-field magnetic susceptibility shows the presence of two maxima at ∼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 = γ + 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 Co²⁺ 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 Co²⁺ ions causes a Schottky-type specific heat anomaly of around 60 K.