Fragile magnetic order in the honeycomb lattice Iridate Na${}_2$IrO${}_3$ revealed by magnetic impurity doping

Abstract

We report the structure, magnetic, and thermal property measurements on single crystalline and polycrystalline samples of Ru substituted honeycomb lattice iridate Na${}_2$Ir${}_x$Ru${}_{1-x}$O${}_3$ (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5). The evolution of magnetism in Na${}_2$Ir${}_x$Ru${}_{1-x}$O${}_3$ has been studied using dc and ac magnetic susceptibility, and heat capacity measurements. The parent compound Na${}_2$IrO${}_3$ is a spin-orbit driven Mott insulator with magnetic order of reduced moments below $T_N=15$~K\@. In the Ru substituted samples the antiferromagnetic long range state is replaced by a spin glass like state even for the smallest substitution suggesting that the magnetic order in Na${}_2$IrO${}_3$ is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na${}_2$IrO${}_3$. Additionally, all samples show insulating electrical transport.

6 pages, 6 figures, 3 tables

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