Induced and cooperative order of Nd ions in NdNiO3

Low-temperature specific heat measurements on NdNiO3 evidence the onset of Nd cooperative ordering at T-N2=0.77 K. Because of the particular arrangement of the Ni magnetic moments, half of the Nd ions have an antiferromagnetically compensated environment while the other half have a noncompensated one. We show that both types of Nd ions are affected by a different but non-negligible Nd-Ni exchange field, in contrast with the current model used in literature. (C) 2000 American Institute of Physics. [S0021- 8979(00)70708-0].