Unusual evolution from a superconducting to an antiferromagnetic ground state in ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ (0 $\le$ $x$ $\le$ 1)

We have studied the evolution of ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ ($0\le x\le 1$) from its superconducting ($x=0$) to antiferromagnetic ($x=1$) states with critical temperatures $T_c=4.6\left(2\right)\mathrm{K}$ and $T_N=15.7\left(2\right)\mathrm{K}$, respectively. At relatively low Gd concentrations ($x\le 0.03$) $T_c$ presents a weak but linear suppression with increasing $x$, as expected from the Abrikosov-Gorkov (AG) theory describing the Cooper pair breaking due to the exchange interaction between the impurity localized magnetic moment and the conduction electrons ($ce$). This linear $T_c$ suppression rate leads to an effective exchange parameter of ${\langle J^2\left(\mathbf{q}\right)\rangle }_{AG}^{1/2}=0.20\left(7\right)\mathrm{meV}$ between the $4f$ localized electrons and the $ce$. For intermediate Gd concentrations ($0.03\le x\le 0.15$), although no Gd clustering is observed, there is an unusual inflection and leveling off trend in $T_c$, indicating that the superconducting phase persists until the highest Gd concentration in this region where magnetic interactions are evidenced by increasingly negative values of the Curie-Weiss temperature ${\mathrm{\Theta }}_C$. Analysis of low-$T{\mathrm{Gd}}^{3+}$ electron spin resonance (ESR) experiments and their ESR line-shape simulations, in conjunction with the trend in $T_c$, leads us to suggest that an exchange bottleneck mechanism between the ${\mathrm{Gd}}^{+3}$ localized magnetic moment and the $ce$ may be the reason behind the inhibition of the Cooper pair-breaking mechanism, in favor of a magnetic interaction via $ce$ polarization. Therefore, our superconducting and ESR results suggest a scenario where superconducting and magnetic phases coexist extensively in the ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ system, mediated by different types of $ce$.

Figure 1

(left) Representation of the cubic unit cell of ${\mathrm{YPb}}_3$ ($a\approx 4.8$ Å) and (right) photo of a typical cubic-shaped single crystal of ${\mathrm{YPb}}_3$ on millimeter paper.

Figure 2

X-ray diffraction pattern of powdered ${\mathrm{YPb}}_3$ crystals showing peaks for the pure phase and for attached Pb flux. The inset shows the evolution of the lattice parameter of ${\mathrm{YPb}}_3$ corresponding to the expected expansion of the unit cell, while the lattice parameter for Pb flux remains unchanged within experimental precision.

Figure 3

SEM image of ${\mathrm{Y}}_{0.93}{\mathrm{Gd}}_{0.07}{\mathrm{Pb}}_3$ with a map of the distribution and relative proportion (intensity) of Y (red) and Pb (yellow) over the scanned area.

Figure 4

The dc magnetization as a function of temperature for ${\mathrm{YPb}}_3$ under different applied magnetic fields. The inset shows an expanded view of the curve for 20 Oe.

Figure 5

Lower critical field $H_{c1}$ and upper critical field $H_{c2}$ as a function of temperature for ${\mathrm{YPb}}_3$. The solid red line represents the fitting of the equation $H_{c1}\left(T\right)=H_{c1}\left(0\right)[1-{(T/T_c)}^2]$. The dashed red line represents a free extrapolation based on the WHH calculation of $H_{c2}\left(0\right)=773\left(20\right)$ Oe (see text).

Figure 6

Evolution of the superconducting temperature $T_c$ as a function of Gd content ($x$ of Gd) in the case of ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ with $0\le x\le 0.16$ compared with the AG trend (blue line). The inset shows the associated value of the Curie-Weiss temperature extracted from dc magnetic susceptibility measurements.

Figure 7

$T$ dependence of the dc magnetic susceptibility $\chi$ of ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ for $x=0.07$, 0.34, 0.63, and 1.0 at $H=10\mathrm{kOe}$. The inset zooms in on the low-$T$ antiferromagnetic transition at $T_N=15.7\left(2\right)\mathrm{K}$ for $x=1.0$.

Figure 8

Gd concentration dependence of the Curie-Weiss temperature of ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ in the full range, $0\le x\le 1$.

Figure 9

$X$-band ${\mathrm{Gd}}^{3+}$ ESR spectra in ${\mathrm{Y}}_{0.985}{\mathrm{Gd}}_{0.015}{\mathrm{Pb}}_3$ at different temperatures and a microwave power of 2 mW. The solid red lines represent the simulated line forms. The inset shows the linewidth evolution with temperature.

Figure 10

$X$-band ${\mathrm{Gd}}^{3+}$ ESR spectra in ${\mathrm{Y}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Pb}}_3$ for $x=0.045$, 0.07, 0.15, and 0.34. The solid red lines represent the simulated line forms. The inset shows the linewidth dependence on temperature for $x=0.07$, 0.15, and 0.34.