Spin-orbit coupling controlled ground states in the double perovskite iridates A2BIrO6 (A = Ba, Sr; B = Lu, Sc)

Abstract

Iridates with the 5$d^4$ electronic configuration have attracted recent interest due to reports of magnetically-ordered ground states despite longstanding expectations that their strong spin-orbit coupling would generate a $J=0$ electronic ground state for each Ir${}^{5+}$ ion. The major focus of prior research has been on the double perovskite iridates Ba${}_2$YIrO${}_6$ and Sr${}_2$YIrO${}_6$, where the nature of the ground states (i.e. ordered vs non-magnetic) is still controversial. Here we present neutron powder diffraction, high energy resolution fluorescence detected x-ray absorption spectroscopy (HERFD-XAS), resonant inelastic x-ray scattering (RIXS), magnetic susceptibility, and muon spin relaxation data on the related double perovskite iridates Ba${}_2$LuIrO${}_6$, Sr${}_2$LuIrO${}_6$, Ba${}_2$ScIrO${}_6$, and Sr${}_2$ScIrO${}_6$ that enable us to gain a general understanding of the electronic and magnetic properties for this family of materials. Our HERFD-XAS and RIXS measurements establish $J=0$ electronic ground states for the Ir${}^{5+}$ ions in all cases, with similar values for Hund's coupling $J_{\mathrm{H}}$ and the spin-orbit coupling constant ${\lambda }_{\mathrm{SOC}}$. Our bulk susceptibility and muon spin relaxation data find no evidence for long-range magnetic order or spin freezing, but they do reveal weak magnetic signals that are consistent with extrinsic local moments. Our results indicate that the large ${\lambda }_{\mathrm{SOC}}$ is the key driving force behind the electronic and magnetic ground states realized in the 5$d^4$ double perovskite iridates, which agrees well with conventional wisdom.

13 pages, 7 figures, accepted for publication by PRM

Cited by in corpus (1)

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