Observation of Nuclear Resonance of Cu in Antiferromagnetic La2CuO4-δand CuO

Abstract

The zero-field nuclear magnetic resonance (NMR) of Cu in the high- T _c related oxide, La ₂ CuO _4-δ , has been observed at 93.85±0.1 MHz for ⁶³ Cu and 100.1±0.1 MHz for ⁶⁵ Cu with well-articulated quadrupole splittings at 1.3 K. The resonance pattern is successfully analyzed as a result of the combined effect of a quadrupole coupling (coupling constant ν _Q =31.9 MHz for ⁶³ Cu and 29.5 MHz for ⁶⁵ Cu with asymmetry parameter η=0.03) and a Zeeman term where the internal field ( H _N =78.78 kOe) is nearly perpendicular to the direction of the maximum electric field gradient (EFG). The quadrupole split zero-field NMR signals have also been observed in CuO. The observed frequencies yield parameter values of 137.1±0.1 MHz, 146.9±0.1 MHz, 20.07 MHz, 18.57 MHz, 0.20, 121.5 kOe, and the direction of H _N is found to be nearly parallel to the direction of the maximum EFG.