Thermodynamic properties of a spin-1/2 diamond chain as a model for a molecule-based ferrimagnet and the compound Cu3(CO3)2(OH)2

The thermodynamic properties of the spin- 1/2 diamond-chain model have been investigated by means of Green's function theory combined with the Jordan-Wigner transformation. According to the different exchange interactions, two typical physical topics are discussed in the paper. (i) Antiferromagnetic (AF)-AF-ferromagnetic (F) ferrimagnetic diamond spin chain as a model for the molecule-based ferrimagnet, which is composed of S=1 biradical and S=1/2 monoradical alternating with antiferromagnetic interactions along the chain, and the S=1 site is composed of two S=1/2 spins by a finite ferromagnetic interaction. The temperature dependence of the specific heat of this model shows remarkable double-peak structure due to the ferromagnetic gapless and antiferromagnetic gap excitation of the spin system, the magnetization curve has a clear plateau at one third of the saturation magnetization, and the susceptibilities exhibit typical ferrimagnetic feature, which is well consistent with experimental findings. (ii) AF-AF-AF frustrated diamond spin chain as a model for the recent thermodynamics measurements on Cu-3(CO3)(2)(OH)(2) by Kikuchi [Phys. Rev. Lett. 94, 227201 (2005)]. The theoretical calculations show that the temperature dependence of magnetic susceptibilities display as a double-peak structure and the specific heat shows a three-peak structure. In particular, the magnetization curve also has a clear plateau at one third of the saturation magnetization with three critical field values H-c1=15.7 T, H-c2=26.5 T, and H-c3=33.6 T, which are in quantitative agreement with the experimental observations.