Thermodynamic properties of a spin-12diamond chain as a model for a molecule-based ferrimagnet and the compoundCu3(CO3)2(OH)2

Abstract

The thermodynamic properties of the spin-$\frac{1}{2}$ 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 ${\mathrm{Cu}}_{3}{(\mathrm{C}{\mathrm{O}}_{3})}_{2}{(\mathrm{O}\mathrm{H})}_{2}$ by Kikuchi et al. [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 ${H}_{\mathrm{c}1}=15.7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, ${H}_{\mathrm{c}2}=26.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, and ${H}_{\mathrm{c}3}=33.6\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, which are in quantitative agreement with the experimental observations.