On Jeff =0 Ground State Iridates(V): Tracking Residual Paramagnetism in New Bi2 NaIrO6.

Abstract

Open-shell transition metal oxides are capable of developing a rich diversity of electronic phases. The specific features evolving crucially depend on an intricate interplay of various local and long-range electronic interactions. Recently, the 5d transition elements have come into sharp focus because for these elements spin-orbit coupling (SOC) and onsite Coulomb repulsion (U) are on a comparable energy scale. For Ir4+ the t2g level associated to an octahedral crystal field (CF) is split by SOC, giving rise to a Jeff = spin state and rendering respective oxides like Sr2 IrO4 as Mott insulators. Transferring this scenario to iridium(V) oxides would lead to a diamagnetic ground state, Jeff =0. However, reported experimental results do not lend unambiguous support for such an electronic state. Theoretical explanations for the breakdown of the J=0 magnetic state suffer from conspicuous discrepancies. In an attempt to empirically contribute to resolving the puzzle, Bi2 NaIrO6 was synthesized in high purity by precipitation from homogeneous solution; it represents an iridium(V) oxide where long range band structure effects and magnetic superexchange are minimized, and the t2g degeneracy is lifted geometrically. We managed to reduce the strength of paramagnetic response, lending support to a Jeff =0 ground state of Bi2 NaIrO6 , exhibiting van Vleck type behavior.