Antiferromagnetism in ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{Cl}}_2$

Magnetic-susceptibility χ(T) and neutron-diffraction studies on single-crystal specimens of ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_2$ ${\mathrm{Cl}}_2$ are reported. A three-dimensional antiferromagnetic structure similar to that in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ is identified below the Néel temperature $T_N$=251±5 K by neutron diffraction, with an ordered moment μ(10 K)=0.34±0.04 ${\mu }_B$/Cu aligned along the [110] crystal direction. This moment is comparable to those for ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ samples with similar $T_N$. No structural transition from the tetragonal I4/mmm space group is observed between 10 and 300 K. The χ(T) near $T_N$ is consistent with the tetragonal structure, showing no evidence for the peak at $T_N$ seen in orthorhombic ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$, arising from the Dzyaloshinsky-Moriya interaction, which is absent without the orthorhombic distortion. Above $T_N$ the exchange coupling constant J between adjacent Cu ions is evaluated from χ(T) and found to be essentially identical to that in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$. The anisotropic Cu spin and Van Vleck susceptibilities are also estimated from the analysis.