HYPERFINE INDUCED NUCLEAR-POLARIZATION IN ND2CUO4

Neutron diffraction investigations of Nd2CuO4 at millikelvin temperatures showed that the intensities of all superstructure Bragg peaks corresponding to the wave vector k = 1/2 1/2 0 strongly increase below about 400 mK. We have interpreted these to be due to the hyperfine induced polarization of the nuclear spins of the Nd-143 and Nd-145 isotopes. By fitting the temperature variation of the intensity of the pure nuclear polarization peak 1/2 1/2 0 to the Brillouin function, we have determined the hyperfine parameter a(0) = (34.6 +/- 0.8) mK. Using this hyperfine parameter a, and the quadrupole coupling constant P determined by NMR experiment (P = 0.11 mK) we have calculated the Schottky anomaly in heat capacity arising from the eight Zeeman-split levels of the nuclear spin I = 7/2 which has a maximum at about T = 34 mK. Heat capacity data at very low temperature should therefore be corrected for the nuclear Schottky anomaly before interpreting electronic and other effects.