HYPERFINE INDUCED NUCLEAR-POLARIZATION IN ND2CUO4

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