F-19 NMR ON PR2CUO4-XFX AND ND2CUO4-XFX

Powders of fluorinated Pr2CuO4 and Nd2CuO4 have been investigated by F -19-NMR using a field- and frequency-step method for magnetic fields B of the order of 4.7 T in the temperature range 400 K > T > 1 K. In co ntrast to the two F-19 resonance lines in fluorine doped Pr2CuO4, only one fluorine resonance is observed in Nd2CuO4, We find a saturation o f the line width and line shift for B/T >> 1 T/K. The results are unam biguously related to the Nd/Pr magnetic moment. Via numerical simulati on of the NMR-spectra the F-sites are selected: the location of the F- ions in Nd2CuO4-xFx is assigned to the O(3) site (0, 0, 0.19). In Pr2C uO4-xFx this position is occupied for 90%; for the second position pos sible locations are indicated.