Magnetic Susceptibility of Ideal Spin 1/2 Heisenberg Antiferromagnetic Chain Systems,Sr2CuO3andSrCuO2
Magnetic susceptibility is measured on the one-dimensional spin 1/2 antiferromagnets ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ and $\mathrm{Sr}{\mathrm{CuO}}_{2}$ using single crystals. Large, nearly contamination-free single crystals enable us to measure the intrinsic spin susceptibility over a wide temperature range between 5 and 800 K. The results are in excellent agreement with the recent calculation by Eggert, Affleck, and Takahashi, and the exchange interaction energy $J$ is estimated to be $2200\ifmmode\pm\else\textpm\fi{}200$ and $2100\ifmmode\pm\else\textpm\fi{}200\mathrm{K}$, respectively. In ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$, an isotropic susceptibility drop is observed below about 20 K, which is also consistent with the result of this rigorous calculation.