NICKEL OXIDATION-STATE AND MAGNETIC-PROPERTIES OF HOLE-DOPED AND REDUCED ND2-XSRXNIOY COMPOUNDS

The Ni K-edge XANES of reduced Nd2-xSrxNiO4 samples shows an increase of Ni3+ content with Sr3+ concentration. The appearance of mixed valen ce Ni2+/Ni3+ produces a change in the magnetic properties of the syste m. The Nd3+ sublattice orders antiferromagnetically at T-N similar to 13-20 K for x = 0.4, 0.5, and 0.6, due to the interactions of Ni-Nd su blattices. For x = 0.8 this order begins to disappear because of the e ffect of the low spin state Ni3+ created at the NiO4 planes. Additiona lly, the reduced family Nd2-xSrxNiOy (y < 4) shows the disappearance o f Ni3+, the decrease of Ni2+ with respect to the nonreduced form, and the appearance of Ni+. All the compounds of the reduced family show AF order at low temperature. (C) 1998 Academic Press.