⁵⁷Fe emission Mossbauer spectroscopy study of single crystal La₂CuO_4-y

Emission Mossbauer studies using a ⁵⁷Co-doped single crystal of La₂CuO_4-y are reported. Measurements have been made at 78 K and at 295 K for different source orientations. Measurements made in the paramagnetic regime (295 K) show that the sign of the electric field gradient (EFG) is positive and that the magnitude of the quadrupole splitting is 1.76 mm s^-1. It is also found that the EFG forms an angle of 39 degrees with respect to the crystalline c axis. Measurements made in the antiferromagnetic regime (78 K) show a Fe hyperfine field of 460 kOe which lies in the basal plane of the crystal structure. These measurements also show an EFG which is positive and in a direction which is consistent with that found in the room temperature measurements. In addition, the magnitude of the quadrupole splitting is consistent with that obtained from the 295 K spectra.