Muon-spin-rotation studies in single-crystal ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{Cl}}_2$

We report zero-field muon-spin-rotation studies on single crystals of ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_2$ ${\mathrm{Cl}}_2$ between 5 and 300 K. Magnetic order below the Néel temperature is observed, and the results are compared with those of neutron diffraction measurements. The temperature dependence of the muon precession frequencies exhibits properties characteristic to two-dimensional spin-1/2 systems with a dominant Heisenberg interaction and very small anisotropy. The splitting of the muon precession frequency below 60 K indicates either a magnetic phase transition or a change in the ${\mathrm{\mu }}^{+}$ site. By comparing the observed static internal field with the calculated dipolar field from ${\mathrm{Cu}}^{2+}$ moments in the crystal we found that the moun sites are located near the center of ${\mathrm{CuO}}_2$ planes.