INFLUENCE OF OXYGEN NONSTOICHIOMETRY ON STRUCTURE AND MAGNETISM IN PR2NIO4+DELTA

The structure and magnetism of Pr2NiO4+ crystals with =0.060 and =0.020 were investigated by neutron scattering. Pr2NiO4.060 is single-phase tetragonal (P42/ncm) from 5 to 300 K with the onset of antiferromagnetic order appearing in the nickel sublattice at TN=116 K, as well as a gradual coupling of praseodymium spins appearing below 80 K. The ordered nickel moment at 10 K is estimated to be 0.62B. Two coexisting phases are observed in the =0.020 sample, apparently resulting from phase separation. Above 118 K, one phase is orthorhombic (Pccn) and the other tetragonal (P42/ncm), with TN=329 and 143 K, respectively. At 118 K, the orthorhombic phase undergoes a transition on cooling to tetragonal P42/ncm symmetry. Spin structures and a magnetic transition are discussed in relation to NiO6 octahedral distortions. © 1990 The American Physical Society.