Microwave and magnetotransport properties of ${\text{RuSr}}_{2}R{\text{Cu}}_2{\text{O}}_8$ $\left(R=\text{Eu},\text{Gd}\right)$ doped with Sn

${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$ and ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the Hall measurements. The ruthenium magnetic ordering temperature $T_m$ is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature $T_c$ accompanied with the increase in the upper critical field $B_{c2}$, indicating an increased disorder in the system and a reduced scattering length of the conducting holes in ${\text{CuO}}_2$ layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in ${\text{CuO}}_2$ layers, which represent the main conductivity channel. Most of the electrons in ${\text{RuO}}_2$ layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in ${\text{RuO}}_2$ layers that exhibit colossal magnetoresistance.

Figure 1

(Color online) Temperature dependence of the normalized surface resistance of (a) ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$ and (b) ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ for various Sn concentrations $x$.

Figure 2

(Color online) Differences in the microwave resistance in zero field and $B=8\text{T}$ of (a) ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$ and (b) ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ for various $x$. (A considerably smaller signal of Sn-doped sample with respect to the pure Gd-based sample is mainly due to the smaller geometry of the former.)

Figure 3

(Color online) Dependence of $T_m$ (open triangles) and $T_c$ (full circles) on $x$ in ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_{2}M{\text{Cu}}_2{\text{O}}_8$, for (a) $R=\text{Eu}$ and (b) $R=\text{Gd}$.

Figure 4

(Color online) Magnetic field dependence of the microwave absorption for (a) ${\text{RuSr}}_2{\text{EuCu}}_2{\text{O}}_8$, (b) ${\text{Ru}}_{0.7}{\text{Sn}}_{0.3}{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$, (c) ${\text{RuSr}}_2{\text{GdCu}}_2{\text{O}}_8$, and (d) ${\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ measured at various temperatures.

Figure 5

(Color online) (a) Dependence of the upper critical field $B_{c2}$ on temperature in ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$, for $x=0$ (squares) and $x=0.3$ (circles). (b) Dependence of $B_{c2}$ on temperature in ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$, for $x=0$ (squares) and $x=0.2$ (circles). (c) Dependence of $B_{c2}$ on $x$ in ${\text{Ru}}_{1-x}{\text{Sn}}_x{\text{Sr}}_2{\text{EuCu}}_2{\text{O}}_8$ at $T=5\text{K}$ (squares) and $T=10\text{K}$ (circles).

Figure 6

(Color online) (a) Resistivity of ${\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ measured in zero field (black line) and in $B=8\text{T}$ (red line). The inset shows the comparison of resistivity with the resistivity of the undoped sample (thin line) (Ref. 16) (b) Difference between the zero-field and 8 T resistivities. The five temperature intervals labeled by (a), (b), (c), (d), and (e) correspond to subsets of MR curves in Fig. 7.

Figure 7

(Color online) Magnetoresistance of ${\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ in various temperature ranges. The values at 43.4 K and 40 K in (e) are divided by factors of 3 and 10, respectively.

Figure 8

(Color online) (a) Magnetic field dependence of the Hall resistivity in ${\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$ at $T=60\text{K}$ (circles) and $T=48\text{K}$ (squares). The Hall resistivity of the undoped ${\text{RuSr}}_2{\text{GdCu}}_2{\text{O}}_8$ at $T=124\text{K}$ is shown by the dotted line for comparison (Ref. 16). (b) Temperature dependence of the low- (open circles) and high-field (full squares) Hall coefficients of ${\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8$. The averaged high-field Hall coefficients of the pure ${\text{RuSr}}_2{\text{GdCu}}_2{\text{O}}_8$ and the La-doped ${\text{RuSr}}_{1.9}{\text{La}}_{0.1}{\text{GdCu}}_2{\text{O}}_8$ are indicated by the arrows for comparison.

Figure 9

(Color online) Field dependence of the quantity $V_0/\left(R_{H}e\right)\left[\Delta {\rho }_{xx}/{\rho }_{xx}\left(0\right)\right]$ for the pure $\left({\text{RuSr}}_2{\text{GdCu}}_2{\text{O}}_8\right)$, Sn-doped $\left({\text{Ru}}_{0.8}{\text{Sn}}_{0.2}{\text{Sr}}_2{\text{GdCu}}_2{\text{O}}_8\right)$ and La-doped $\left({\text{RuSr}}_{1.9}{\text{La}}_{0.1}{\text{GdCu}}_2{\text{O}}_8\right)$ samples at their respective magnetic ordering temperatures.