  We report a comprehensive investigation of Ln2NiIrO6 (Ln = La, Pr, Nd) using
thermodynamic and transport properties, neutron powder diffraction, resonant
inelastic x-ray scattering, and density functional theory (DFT) calculations to
investigate the role of A-site cations on the magnetic interactions in this
family of hybrid 3d-5d-4f compositions. Magnetic structure determination using
neutron diffraction reveals antiferromagnetism for La2NiIrO6, a collinear
ferrimagnetic Ni/Ir state that is driven to long range antiferromagnetism upon
the onset of Nd ordering in Nd2NiIrO6, and a non-collinear ferrimagnetic Ni/Ir
sublattice interpenetrated by a ferromagnetic Pr lattice for Pr2NiIrO6. For
Pr2NiIrO6 heat capacity results reveal the presence of two independent magnetic
sublattices and transport resistivity indicates insulating behavior and a
conduction pathway that is thermally mediated. First principles DFT calculation
elucidates the existence of the two independent magnetic sublattices within
Pr2NiIrO6 and offers insight into the behavior in La2NiIrO6 and Nd2NiIrO6.
Resonant inelastic x-ray scattering is consistent with spin-orbit coupling
splitting the t2g manifold of octahedral Ir4+ into a Jeff = 1/2 and Jeff = 3/2
state for all members of the series considered.
