ANTIFERROMAGNETISM IN SR2CUO2CL2

Magnetic-susceptibility (T) and neutron-diffraction studies on single-crystal specimens of Sr2CuO2Cl2 are reported. A three-dimensional antiferromagnetic structure similar to that in La2CuO4 is identified below the Néel temperature TN=2515 K by neutron diffraction, with an ordered moment (10 K)=0.340.04 B/Cu aligned along the [110] crystal direction. This moment is comparable to those for La2CuO4 samples with similar TN. No structural transition from the tetragonal I4/mmm space group is observed between 10 and 300 K. The (T) near TN is consistent with the tetragonal structure, showing no evidence for the peak at TN seen in orthorhombic La2CuO4, arising from the Dzyaloshinsky-Moriya interaction, which is absent without the orthorhombic distortion. Above TN the exchange coupling constant J between adjacent Cu ions is evaluated from (T) and found to be essentially identical to that in La2CuO4. The anisotropic Cu spin and Van Vleck susceptibilities are also estimated from the analysis. © 1990 The American Physical Society.