Tipping the magnetic instability in paramagnetic $\mathrm{S}{\mathrm{r}}_3\mathrm{R}{\mathrm{u}}_2{\mathrm{O}}_7$ by Fe impurities

We report the magnetic and electronic properties of the bilayer ruthenate $\mathrm{S}{\mathrm{r}}_3\mathrm{R}{\mathrm{u}}_2{\mathrm{O}}_7$ upon Fe substitution for Ru. We find that $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ shows a spin-glass-like phase below 4 K for $x=0.01$ and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector ${\mathbf{q}}_{\mathrm{c}}=\left(0.250.250\right)$ for $x\ge 0.03$, respectively, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors $\mathbf{q}=\left(0.0900\right)$ and (0.25 0 0). The observed antiferromagnetic ordering is quasi-two-dimensional with very short correlation length along the $c$ axis, a feature similar to the Mn-doped $\mathrm{S}{\mathrm{r}}_3\mathrm{R}{\mathrm{u}}_2{\mathrm{O}}_7$. Our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the $3d$ orbitals of the magnetic dopants and Ru $4d$ orbitals.

Figure 1

(a) and (b) Temperature dependence of the magnetic susceptibility ${\chi }_{\mathrm{c}}$ of $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ ($x=0.01$ and 0.03) after ZFC and FC. Insets show the in-plane magnetic susceptibility ${\chi }_{\mathrm{ab}}$ as a function of temperature after ZFC and FC. (c) and (d) Isothermal magnetization as a function of the magnetic field of $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ ($x=0.01$ and 0.03), respectively. The field is applied along the $c$ axis. Inset shows the data of the $x=0.01$ compound at 2 K up to 9 T.

Figure 2

(a) Specific heat of $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ as a function of temperature for $x=0.01$ and 0.03. The blue arrow denotes the Nèel temperature $T_{\mathrm{N}}$ obtained from the magnetic susceptibility measurements. (b) In-plane resistivity ${\rho }_{\mathrm{ab}}$ of $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ as a function of temperature. Inset shows ${\rho }_{\mathrm{ab}}$ vs $T^2$ in the low temperature regime for $x=0.01$. The red line is a fit using linear function.

Figure 3

Neutron diffraction data of $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ ($x=0.03$). (a) Radial scans around ${\mathbf{q}}_{\mathrm{c}}=\left(0.250.250\right)$ along the [1 1 0] direction at representative temperatures. $H$ is in reduced lattice unit. (b) Temperature dependence of the peak intensity of ${\mathbf{q}}_{\mathrm{c}}=\left(0.250.250\right)$ showing the magnetic ordering at $T_{\mathrm{N}}\sim 40\mathrm{K}$. (c) and (d) Scans around ${\mathbf{q}}_{\mathrm{c}}=\left(0.250.250\right)$ and (0.75 0.75 0) along the [0 0 1] direction, respectively. $L$ is in reduced lattice unit.

Figure 4

(a) Schematic of the E-type antiferromagnetic order of one bilayer in $\mathrm{S}{\mathrm{r}}_3{\left(\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{F}{\mathrm{e}}_x\right)}_2{\mathrm{O}}_7$ ($x=0.03$). (b) Synchrotron x-ray absorption measurements on Fe-doped $\mathrm{S}{\mathrm{r}}_3\mathrm{R}{\mathrm{u}}_2{\mathrm{O}}_7$ ($x=0.03$) and the reference samples FeO ($\mathrm{F}{\mathrm{e}}^{2+}$) and $\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$ ($\mathrm{F}{\mathrm{e}}^{3+}$).