HYPERFINE-ENHANCED NUCLEAR-POLARIZATION IN NDGAO3

The three-dimensional magnetic ordering of the Nd3+ ions in NdGaO3 has been studied by means of neutron powder diffraction. The transition to the antiferromagnetic state takes place at T-N approximate to 1 K. Below this temperature, the Nd3+ magnetic moments are oriented along the c axis in a c(z) mode. The value of the saturated magnetic moment (approximate to 1.1 mu(B)) is drastically reduced below the free ion value (3.27 mu(B)) due to crystal-field effects. The main contribution to the Nd-Nd magnetic interaction appears to be superexchange, the classical dipole-dipole interaction being too small to account for the observed Neel temperature. Below 300 mM, we observe an additional enhancement of the magnetic reflections. The analysis of the Q dependence of the neutron powder-diffraction intensities allowed us to interpret this increase as due to the polarization of the nuclear moments of the Nd-143 and Nd-145 isotopes in the hyperfine field created by the Nd3+ electronic moments. The particular conditions which lead to the observation of this phenomenon in NdGaO3 are briefly discussed.