Spin-orbit effects in pentavalent Iridates: Models and materials

Abstract

Spin-orbit effects in heavy 5$d$ transition metal oxides, in particular, iridates, have received enormous current interest due to the prediction as well as the realization of a plethora of exotic and unconventional magnetic properties. While a bulk of these works are based on tetravalent iridates ($d^5$), where the counter-intuitive insulating state of the rather extended 5$d$ orbitals are explained by invoking strong spin-orbit coupling, the recent quest in iridate research has shifted to the other valencies of Ir, of which pentavalent iridates constitute a notable representative. In contrast to the tetravalent iridates, spin-orbit entangled electrons in $d^4$ systems are expected to be confined to the $J=0$ singlet state without any resultant moment or magnetic response. However, it has been recently predicted that, magnetism in $d^4$ systems may occur via magnetic condensation of excitations across spin-orbit-coupled states. In reality, the magnetism in Ir${}^{5+}$ systems are often quite debatable both from theoretical as well as experimental point of view. Here we provide a comprehensive overview of the spin-orbit coupled $d^4$ model systems and its implications in the studied pentavalent iridates. In particular, we review here the current experimental and theoretical understanding of the double perovskite ($A_{2}B$YIrO${}_6$, $A=$ Sr, Ba, $B=$Y, Sc, Gd), 6H-perovskite (Ba${}_{3}M$Ir${}_2$O${}_9$, $M=$ Zn, Mg, Sr, Ca), post-perovskite (NaIrO${}_3$), and Hexagonal (Sr${}_3$MIrO${}_6$) iridates, along with a number of open questions that require future investigation.

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Cited by in corpus (2)

• $J_{eff}$ states in a quasi one dimensional antiferromagnetic spin chain hexagonal Iridates Sr${}_3$MIrO${}_6$ (M=Mg, Zn, Cd): an $ab-initio$ comparative perspective
• Jahn-Teller states mixed by spin-orbit coupling in an electromagnetic field