New Insulating Antiferromagnetic Quaternary Iridates MLa10Ir4O24 (M = Sr, Ba).

Qingbiao Zhao,J F Mitchell,Fei Han,Tian-Heng Han,Constantinos C Stoumpos,Hao Li

doi:10.1038/srep11705

Abstract

Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator.

Highlights

Oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = 1⁄2, that defines the electronic and magnetic properties
Lattice constants and space group (I41/a) extracted from single-crystal diffraction measurements were similar to that of the known compound Sr9La2Mo4O2413, and the crystal structures of the iridates could be solved from this starting model
It is known that some fluxes like KOH can dissolve O2 from the atmosphere to provide an oxidizing environment; mostly Ir(V) compounds have been synthesized from KOH flux, but some Ir(VI) and Ir(V) oxides are reported[29,30]

Summary

Introduction

Some known iridates, including Ba2IrO411 and Ca4IrO612, have already shown behavior consistent with a Jeff = 1⁄2 description by resonant inelastic X-ray scattering, indicating that the phase space of Jeff = 1⁄2 materials extends beyond Sr2IrO4 These discoveries underscore the importance of identifying new iridates with Jeff = 1⁄2 states to better understand the phenomenology of these unusual correlated oxides. The scope of the present work lies firmly in the regime of discovery synthesis of new compounds in a relatively unexplored regime of crystal chemistry as a first step on the way to classifying and understanding the breadth of spin-orbit driven physics in iridates Toward this end, we have synthesized two new isostructural tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba) and characterized their crystal structures and magnetic, transport, and thermodynamic signatures. It is demonstrated that high order iridates can be made with a facile flux crystal growth approach

Methods

Results

Discussion

Conclusion