Dilution of the magnetic lattice in the Kitaev candidate $\alpha$-RuCl$_3$ by Rh$^{3+}$ doping

TL;DR

This study investigates how substituting Rh for Ru in $ ext{RuCl}_3$ affects its magnetic properties, revealing suppression of magnetic order at moderate doping levels and insights into the robustness of its magnetic ground state.

Contribution

It provides the first detailed phase diagram of Rh-doped $ ext{RuCl}_3$, showing magnetic order suppression and comparing effects with Ir doping, highlighting the role of chemical pressure.

Findings

Magnetic order suppressed at $x \\approx 0.2$

Disordered phase without spin glass behavior

Magnetic properties slightly affected by thermal cycling

Abstract

Magnetic dilution of a well-established Kitaev candidate system is realized in the substitutional Ru$_{1-x}$Rh$_x$Cl$_3$ series ($x = 0.02-0.6$). Optimized syntheses protocols yield uniformly-doped single crystals and polycrystalline powders that are isostructural to the parental $\alpha$-RuCl$_3$ as per X-ray diffraction. The Rh content $x$ is accurately determined by the quantitative energy-dispersive X-ray spectroscopy technique with standards. We determine the magnetic phase diagram of Ru$_{1-x}$Rh$_x$Cl$_3$ for in-plane magnetic fields from magnetization and specific-heat measurements as a function of $x$ and stacking periodicity, and identify the suppression of the magnetic order at $x \approx 0.2$ towards a disordered phase, which does not show any clear signature of freezing into a spin glass. Comparing with previous studies on the substitution series Ru$_{1-x}$Ir$_x$Cl$_3$, we propose that chemical pressure would contribute to the suppression of magnetic order especially in Ru$_{1-x}$Ir$_x$Cl$_3$ and that the zigzag magnetic ground state appears to be relatively robust with respect to the dilution of the Kitaev--$\Gamma$--Heisenberg magnetic lattice. We also discovered a slight dependence of the magnetic properties on thermal cycling, which would be due to an incomplete structural transition.