Antiferromagnetism in Sr2CuO2Cl2.

Abstract

Magnetic-susceptibility \ensuremath{\chi}(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}$${\mathrm{CuO}}_{4}$ is identified below the N\'eel temperature ${T}_{N}$=251\ifmmode\pm\else\textpm\fi{}5 K by neutron diffraction, with an ordered moment \ensuremath{\mu}(10 K)=0.34\ifmmode\pm\else\textpm\fi{}0.04 ${\ensuremath{\mu}}_{B}$/Cu aligned along the [110] crystal direction. This moment is comparable to those for ${\mathrm{La}}_{2}$${\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 \ensuremath{\chi}(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}$${\mathrm{CuO}}_{4}$, arising from the Dzyaloshinsky-Moriya interaction, which is absent without the orthorhombic distortion. Above ${T}_{N}$ the exchange coupling constant J between adjacent Cu ions is evaluated from \ensuremath{\chi}(T) and found to be essentially identical to that in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. The anisotropic Cu spin and Van Vleck susceptibilities are also estimated from the analysis.