Observation of Antiferromagnetic Nuclear Resonance of Cu in YBa2Cu3O6

The zero-field antiferromagnetic nuclear resonance (AFNR) of Cu in the high- T c related oxide YBa 2 Cu 3 O 6 has been observed at 89.89±0.05 MHz for 63 Cu and 96.29±0.05 MHz for 65 Cu with well articulated quadrupole splittings at 1.3 K. These frequencies correspond to a hyperfine field of 79.65±0.05 KOe. From the analysis of the AFNR spectrum and the observation of NQR at 30.11±0.2 MHz for 65 Cu and 27.88±0.02 MHz for 63 Cu, both of which have no Zeeman splitting, it is concluded that the antiferromagnetic mounents reside only on the CuO 2 plane sites and the direction of moments is perpendicular to the c -axis. This is consistent with the spin structure proposed by neutron diffraction studies. The nuclear relaxation behavior is also discussed briefly.