MAGNETIC-SUSCEPTIBILITY AND LOW-TEMPERATURE STRUCTURE OF THE LINEAR-CHAIN CUPRATE SR2CUO3

Magnetic susceptibility measurements for Sr2CuO3 were made from 2 to 800 K, and a strong dependence upon oxygen content () was observed. Samples synthesized under oxygen, followed by various nitrogen treatments, exhibited markedly different Curie-Weiss-type terms, and we discuss possible origins for this behavior. High-temperature magnetic susceptibility measurements for the sample with the smallest Curie-Weiss-type term clearly show the increase with temperature expected from the Bonner-Fisher model for a spin-1/2 one-dimensional (1D) Heisenberg antiferromagnet. This is a direct experimental observation of 1D magnetic behavior in this system. The in-chain superexchange coupling constant, as determined by a fit to the Bonner-Fisher model, is J/kB 1300-200+100 K, comparable to the values observed in the two-dimensional layered cuprates. Estimates of the interchain magnetic interaction indicate this material may be the best realization of a 1D spin-1/2 Heisenberg antiferromagnet reported to date. Low-temperature neutron and synchrotron x-ray powder-diffraction studies of Sr2CuO3 show that the low-temperature structure of this system has Immm space-group symmetry, the same structure reported at room temperature, indicating that this material, in contrast to La2CuO4, does not undergo any structural transformations upon cooling. The absence of crystallographic distortions precludes a magnetic anisotropy contribution from a Dzyaloshinsky-Moriya interaction, implying that Sr2CuO3 should be a nearly ideal spin-1/2 antiferromagnetic Heisenberg chain compound, in agreement with the magnetic susceptibility results. A search for the presence of long-range three-dimensional antiferromagnetic order by magnetic neutron powder diffraction at temperatures as low as 1.5 K was not successful, although we estimate an upper limit for the size of the ordered moment which could have been detected to be 0.1 B per Cu2+ ion. © 1995 The American Physical Society.