${\mathrm{BaCu}}_2{\mathrm{V}}_2{\mathrm{O}}_8$: Quasi-one-dimensional alternating chain compound with a large spin gap

The new quasi-one-dimensional spin gap compound ${\mathrm{BaCu}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ was studied by means of magnetic susceptibility and heat capacity measurements on a powder sample. The magnetic susceptibility was well reproduced by alternating antiferromagnetic chain model with $J_1=260\mathrm{K}$ and $J_2=52\mathrm{K}$, which result in a large spin gap of about $230\mathrm{K}$. It is suggested that the $J_1$ and $J_2$ are ascribable to interactions along the $\mathrm{Cu}\text{−}\mathrm{O}\text{−}\mathrm{V}\text{−}\mathrm{O}\text{−}\mathrm{Cu}$ path and the $\mathrm{Cu}\text{−}\mathrm{O}\text{−}\mathrm{Cu}$ path, respectively.

Figure 1

(Color online) The crystal structure of ${\mathrm{BaCu}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ $\left(0.5a\times 0.5b\times 2.5c\right)$. (a) The ${\mathrm{V}}^{5+}$ ions have two crystallographic sites ${\mathrm{V}}_1$ and ${\mathrm{V}}_2$, corresponding to the ${\mathrm{VO}}_4$ tetrahedra, (dark) and (light). (b) Two interaction paths, $\left(J_1\right)$ and $\left(J_2\right)$, of the linear chain built by ${\mathrm{VO}}_4$ tetrahedra $\left({\mathrm{V}}_1\right)$ and edge-sharing pairs of ${\mathrm{CuO}}_4$ square-plaquettes along the $c$-axis.

Figure 2

(Color online) Temperature dependence of magnetic susceptibility of ${\mathrm{BaCu}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ from $900\mathrm{K}$ to $2\mathrm{K}$. The big open circles represent the observed raw data, the small open circles are the data after subtraction of the Curie-term. The thick solid line represents the result of fitting to the equation, $\chi \left(T\right)={\chi }_0+{\chi }_{\mathrm{cw}}\left(T\right)+{\chi }_{\text{spin}}\left(T\right)$ below $120\mathrm{K}$. The thin solid line represents the result of fitting to the chain model given by Hatfield above $120\mathrm{K}$. The dashed line represents the Curie-term. The inset shows a comparison of fitted results between the isolated dimer model and the chain model. The closed circles represent the observed data, the solid line the fitted result by the chain model, and the dashed line the fitted result by the isolated dimer model.

Figure 3

(Color online) Magnetization $\left(M\right)$ vs applied field $\left(H\right)$ at $2\mathrm{K}$. The open circles represent the observed raw data, the solid line the fitted value by a Brillouin-function of $S=1∕2$.

Figure 4

(Color online) Heat capacity of ${\mathrm{BaCu}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ as a function of temperature. The inset shows $C_p∕T$ vs $T$, a comparison of heat capacities measured under the fields 0 and $9\mathrm{T}$ below $8\mathrm{K}$.