Evolution of structure, magnetism, and electronic transport in the doped pyrochlore iridate ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$

The interplay between spin-orbit coupling (SOC) and electron correlation ($U$) is considered for many exotic phenomena in iridium oxides. We have investigated the evolution of structural, magnetic, and electronic properties in the pyrochlore iridate ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ where the substitution of Ru has been aimed to tune this interplay. The Ru substitution does not introduce any structural phase transition, however, we do observe an evolution of lattice parameters with the doping level $x$. X-ray photoemission spectroscopy (XPS) study indicates Ru adopts the charge state of ${\mathrm{Ru}}^{4+}$ and replaces the ${\mathrm{Ir}}^{4+}$ accordingly. Magnetization data reveal both the onset of magnetic irreversibility and the magnetic moment decreases with progressive substitution of Ru. These materials show a nonequilibrium low temperature magnetic state as revealed by magnetic relaxation data. Interestingly, we find the magnetic relaxation rate increases with substitution of Ru. The electrical resistivity shows an insulating behavior in the whole temperature range, however, resistivity decreases with the substitution of Ru. The nature of electronic conduction has been found to follow power-law behavior for all the materials.

Figure 1

Room temperature XRD pattern along with Rietveld analysis have been shown for representative (a) $x=0.0$ and (b) $x=0.4$ composition for the ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ series.

Figure 2

(a) Lattice constant $a$, (b) $x$ position of O1 atom, (c) Ir-O1 bond length, and (d) Ir-O1-Ir bond angle are shown as a function of Ru substitution for the ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ series. Lines are a guide to the eyes.

Figure 3

XPS spectra related to (a) $\mathrm{Ir}-4f$ and (b) $\mathrm{Y}-3p$ level are shown for the parent ${\mathrm{Y}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ (YIO) material. Open black circles are the XPS data. The red solid line in (a) is the fitted envelope taking contributions of ${\mathrm{Ir}}^{4+}$ and ${\mathrm{Ir}}^{5+}$ components which are individually plotted in dashed blue and green colors, respectively. (c) and (d) show the same XPS data and related fittings for doped ${\mathrm{Y}}_2{\mathrm{Ir}}_{1.6}{\mathrm{Ru}}_{0.4}{\mathrm{O}}_7$ (RuYIO) material.

Figure 4

Temperature dependent magnetization data measured in 1 kOe under ZFC and FC protocol have been shown for the ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ series. Filled and unfilled symbols represent ZFC and FC data, respectively. Inset shows variation of irreversibility temperature $T_{irr}$ with Ru substitution for the same series.

Figure 5

Temperature dependent inverse susceptibility $[{\chi }^{-1}={(M/H)}^{-1}]$ as deduced from magnetization data in Fig. 4 are shown with (a) $x$ = 0.0, 0.1 and (b) $x$ = 0.2, 0.4 composition for the ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ series. The solid lines are due to fitting using Eq. (1). The arrows indicate the $T_{irr}$ of corresponding materials.

Figure 6

(a) Magnetic field dependent magnetization are shown for ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ at 5 K. (b) The M(H) data are plotted in the form of Arrott plot ($M^2$ vs $H/M$) for the same materials.

Figure 7

(a) The normalized magnetic moment $M\left(t\right)/M\left(0\right)$ as a function of time has been shown for $x=0.0$ and 0.2 with $t_w={10}^2$ s. (b) The similar normalized moment has been shown for different wait time $t_w$ for ${\mathrm{Y}}_2{\mathrm{Ir}}_{1.6}{\mathrm{Ru}}_0.4{\mathrm{O}}_7$. The solid lines show representative fitting of data using Eq. 2.

Figure 8

(a) Temperature dependent resistivity data of the ${\mathrm{Y}}_2{\mathrm{Ir}}_{2-x}{\mathrm{Ru}}_x{\mathrm{O}}_7$ series are shown in a semilog plot. (b) The $\rho \left(T\right)$ data in (a) are plotted in the $ln-ln$ plot. The solid lines are due to a fitting with Eq. 3.