Bulk Magnetic Order in a Two-Dimensional Ni1+/Ni2+ (d9/d8) Nickelate, Isoelectronic with Superconducting Cuprates

The Ni¹⁺/Ni²⁺ states of nickelates have the identical (3d⁹/3d⁸) electronic configuration as Cu²⁺/Cu³⁺ in the high temperature superconducting cuprates, and are expected to show interesting properties. An intriguing question is whether mimicking the electronic and structural features of cuprates would also result in superconductivity in nickelates. Here we report experimental evidence for a bulklike magnetic transition in La₄Ni₃O₈ at 105 K. Density functional theory calculations relate the transition to a spin density wave nesting instability of the Fermi surface.