Impurity effects on the Ni³⁺ triangular lattice of Ag₂NiO₂

Silver oxonickelate Ag₂NiO₂ is a metallic compound presenting a spin-1/2 triangular lattice. It exhibits a structural transition at T_s = 260 K, which may be related to e_g orbital ordering, and an antiferromagnetic transition at T_N = 55 K. Impurity effects on its magnetic and electronic properties are examined by substituting Fe for Ni in Ag₂Ni_1−xFe_xO₂ (0≤x≤0.3). A Curie-like enhancement in magnetic susceptibility is observed at low temperature, which implies that most Fe³⁺ spins behave as free spins. Moreover, a large enhancement of residual resistivity and its suppression under magnetic fields are observed. Magnetic interactions in the Ni³⁺ triangular lattice are discussed.