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Magnetic susceptibility is measured on the one-dimensional spin 1͞2 antiferromagnets Sr 2 CuO 3 and SrCuO 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 6 200 and 2100 6 200 K, respectively. In Sr 2 CuO 3 , an isotropic susceptibility drop is observed below about 20 K, which is also consistent with the result of this rigorous calculation. PACS numbers: 75.40.Cx, 75.10.Jm It is well known that one-dimensional (1D) quantum spin systems are expected to show many interesting magnetic properties originating from the low dimensionality and the quantum fluctuations. In particular, theoretical studies on these systems have achieved remarkable progress. After the exact evaluation of the value of the magnetic susceptibility at zero temperature [1], Bonner and Fisher (BF) [2] calculated the magnetic susceptibility of the S 1͞2 finite-length chain numerically, which is a good approximation at high temperatures and has been used to compare the experimental results of real materials. Recently, by applying conformal field theory, Eggert, Affleck, and Takahashi (EAT) have succeeded in calculating the magnetic susceptibility of the S 1͞2 antiferromagnetic (AF) Heisenberg spin chain system with high accuracy [3]. Their result has revealed a characteristic temperature dependence of the magnetic susceptibility at low temperatures as low as 0.01J. Considering such theoretical progress, it is indispensable to evaluate the magnetic properties of 1D S 1͞2 AF systems over a wide temperature range using well-characterized single crystals.In this Letter, we study the magnetic susceptibility of Sr 2 CuO 3 and SrCuO 2 single crystals, which turns out to be almost ideal systems of 1D S 1͞2 AF Heisenberg chains. The result can be quantitatively compared with the recent theoretical calculation. It is shown that the experimental results are in excellent agreement with the theoretical calculation, and the exchange interaction J is estimated to be 2200 6 200 K for Sr 2 CuO 3 and 2100 6 200 K for SrCuO 2 , respectively. In particular, Sr 2 CuO 3 exhibits a characteristic temperature dependence at low temperatures (T , 0.01J) as predicted by EAT.Sr 2 CuO 3 has the 1D chains composed of these CuO 4 quadrilateral structures with sharing corner oxygens together [ Fig. 2(a)] [4]. The exchange interaction J between neighboring Cu 21 ions is expected to be large because of the superexchange interaction. In the previous study using polycrystalline samples, the J value was estimated to be more than 1000 K [5,6]. In spite of this large J value, the mSR experiment [5] shows that this material has the three-dimensional (3D) long range AF order only below T N ϳ 5 K; moreover recent neutron scattering measurements using the same single crystal used in the present stud...

The electronic states and magnetic properties for the copper oxides containing edge-sharing Cu-O chains such as Li2CuO2, La6Ca8Cu24O41 and CuGeO3 are systematically studied. The optical conductivity (!) and the temperature dependence of the magnetic susceptibility (T ) for single crystalline samples Li2CuO2 are measured as a reference system and analyzed by using the exact diagonalization method for small Cu-O clusters. It is shown that the spectral distribution of (!) is dierent between edge-sharing and corner-sharing Cu-O-Cu bonds. The charge transfer gap in edge-sharing chains is larger than that of high-T c cuprates. The exchange interaction between nearest-neighbor copper ions in edge-sharing chains J1 depends sensitively on the Cu-O-Cu bond angles. In addition to J1, the exchange interaction between next-nearest-neighbor copper ions J2 has sucient contribution to the magnetic properties. We calculate J 1 and J 2 for all the copper oxides contaning edge-sharing Cu-O chains and discuss the magnetic properties. PACS appear here. npacsfg should always be input, even if empty.

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