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 approximately 8 and 4 K (Tf), 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 (Cmag) shows a lack of any long-range ordered peaks. Instead, a broad maximum near Tf was observed in the Cma)(T)/T-curve. Below Tf, the Cmag(T) data follow the relation: Cmag(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 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.

Frustrations and orderings in Ising chain with multiple interactions

“…Note that the peak splitting described above in three scenarios during the temperature evolution of the magnetic contribution to heat capacity is observed in real rare-earth antiferromagnets [7,[41][42][43][44][45][46][47][48] and actinide compounds [49], as well as a number of organometallic coordination polymers [50,51], molecular [52] and quasi-one-dimensional frustrated [53] magnets.…”

“…where the argument of the natural logarithm is the statistical weight of the system, which is defined as the maximum real root of the corresponding equation. Thus for residual entropy (50) this equation has the form…”

“…The frustrations exist in the considered interval of values of the variables of the model. At first, frustrations arise at a point corresponding to the ratio of the exchange interaction parameters of the model (J 2 = J 1 /2 and J 3 = 0), at which the value of residual entropy is greater than zero and equal to the value (50).…”

Dielectric properties of Co(CO3)(H2O)2(C3H4N2)2 and [Co(C3H3N2)2]n

“…6) and [Co(C 3 H 3 N 2 ) 2 ] n . 7 The experimental data revealed that the Co 2+ ions in these compounds behave in a different manner. In the rst complex, due to an unquenched spin-orbit coupling the Co 2+ ions exhibit a large effective magnetic moment of 5.15 m B .…”

“…Sample preparation procedures and their characterization were described in detail before. 6,7 These samples, henceforth abbreviated as Co(CO 3 )(OH 2 ) 2 (ImH) 2 and Co(Im) 2 , respectively. In this work, we present the results of measurements on two samples of Co(Im) 2 labelled as Nr 1 and Nr 2 and compare the data with that of Co(CO 3 )(H 2 O) 2 (ImH) 2 .…”