TRANSPORT AND MAGNETIC-PROPERTIES VERSUS HOLE DOPING IN (LA,ND)2NIO4+DELTA

We report a preliminary study of the magnetic and transport properties of some hole-doped Ln2-x Srx NiO4+δ, oxides (Ln = La, Nd). An antiferromagnetic ordering is found for stoichiometric oxides with a WF transition at 80K (La NiO4) and 130K (Nd2 NiO4). In Nd2NiO4 at lower temperatures, two additional magnetic reorientation are found. At 11K a long range magnetic order of the Nd ions sets in. Magnetic susceptibility measurements of hole-doped samples reveal that above a certain temperature T* a Curie-Weiss law is found. The corresponding magnetic moments appear to be independent of the hole concentration and close that expected for Ni2 ions. This is actually an evidence of the O(2p) character of these holes. In this high-temperature range, thermopower measurements signal hole-like charge carriers and activated conductivity. Below T*, localization of holes as observed from transport data, leads to a strong AF Ni2+-O- interaction. which frustrates the otherwise AF Ni2+-Ni2+ interaction. © 1990.