Magnetic Susceptibility of Ideal Spin 1 /2 Heisenberg Antiferromagnetic Chain Systems, Sr₂CuO₃ and SrCuO₂

Magnetic susceptibility is measured on the one-dimensional spin 1/2 antiferromagnets Sr₂CuO₃ and SrCuO₂ 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±200 and 2100±200K, respectively. In Sr₂CuO₃, an isotropic susceptibility drop is observed below about 20 K, which is also consistent with the result of this rigorous calculation.