| Popis: |
High-temperature series expansions were applied to the magnetic susceptibility of the quasilayered "eclipsed" compounds $[\mathrm{N}{\mathrm{H}}_{3}{(\mathrm{C}{\mathrm{H}}_{2})}_{n}\mathrm{N}{\mathrm{H}}_{3}]\mathrm{Cu}{\mathrm{Br}}_{4}$ for $n=3 \mathrm{and} 4$ to determine the interplanar, ${J}_{2h}$, and intraplanar, ${J}_{1h}$, exchange and to test the predictions of the importance of the halide-halide separation in two-halide superexchange. The results are $\frac{{J}_{1h}}{{k}_{B}}=26 \mathrm{and} 29$ K, $\frac{{J}_{2h}}{{k}_{B}}=\ensuremath{-}26 \mathrm{and} \ensuremath{-}5$ K, respectively, while transitions to long-range order are estimated to occur at 40 and 19 K. The strength of the exchange interaction as a function of halide separation through the linear two-bromine bridge between planes is shown to be $J\ensuremath{\propto}{d}^{\ensuremath{-}11\ifmmode\pm\else\textpm\fi{}3}$ which agrees with the earlier results for the isostructural ${\mathrm{Cl}}_{4}$ compounds. |
