From Ising Resonant Fluctuations to Static Uniaxial Order in Antiferromagnetic and Weakly Superconducting $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Hg}}_x{)}_5(x=0.01)$

$\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$ is a charge doped variant of the $d$-wave ${\mathrm{CoCoIn}}_5$ superconductor with coexistent antiferromagnetic and superconducting transitions occurring at $T_N=3.4$ and $T_c=1.4\mathrm{K}$, respectively. We use neutron diffraction and spectroscopy to show that the magnetic resonant fluctuations present in the parent superconducting phase are replaced by collinear $c$-axis magnetic order with three-dimensional Ising critical fluctuations. No low-energy transverse spin fluctuations are observable in this doping-induced antiferromagnetic phase and the dynamic resonant spectral weight predominately shifts to the elastic channel. Static ($\tau >0.2\mathrm{ns}$) collinear Ising order is proximate to superconductivity in ${\mathrm{CeCoIn}}_5$ and is stabilized through hole doping with Hg.

Figure 1

The magnetic Bragg peak intensity measured as a function of temperature in superconducting and antiferromagnetic (a) $\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$, (b) $\mathrm{CeCo}({\mathrm{In}}_{0.987}{\mathrm{Hg}}_{0.013}{)}_5$, and (c) magnetic helically ordered and nonsuperconducting ${\mathrm{CeRhIn}}_5$ (from Ref. [33]). The SC transition $T_c$ and Néel $T_N$ temperatures are indicated by vertical lines. (d) Temperature composition $T-x$ phase diagram of $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Hg}}_x{)}_5$ determined from specific heat measurements.

Figure 2

Constant $\overrightarrow{Q}=(1/2,1/2,1/2)$ scans for superconducting (a) ${\mathrm{CeCoIn}}_5$ and superconducting and antiferromagnetic (b) $\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$ with both plots normalized to the same absolute scale. Panel (c) illustrates the critical magnetic fluctuations showing polarization along $c$ and (d) antiferromagnetic correlations within the $a\text{−}b$ plane of $\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$. The solid lines in (c) and (d) are fits to Eq. (1) corresponding to ${\mathrm{Ce}}^{3+}$ moments polarized along the [001] direction. The dashed line is the same fit to a model with the isotropic magnetic moments having no preferential direction.

Figure 3

(a) Constant $\overrightarrow{Q}=(H,H,1/2)$ slice and constant energy slices at (b) 0.5 and (c) 1.0 meV of $\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$ at 3.5 K.

Figure 4

The temperature dependence of the magnetic critical scattering in $\mathrm{CeCo}({\mathrm{In}}_{0.990}{\mathrm{Hg}}_{0.010}{)}_5$. (a)–(b) illustrate constant $E=0.5\mathrm{meV}$ slices in the (HHL) scattering plane taken at 7.5 and 13 K, respectively. (c) Intensity of the $\overrightarrow{Q}=(1/2,1/2,1/2)$ magnetic position as a function of temperature. (d)–(e) illustrate high resolution backscattering measurements probing the temporal nature of the magnetic order. The horizontal bar is the energy resolution showing that the magnetic order is static to within an energy resolution of $25\mu \mathrm{eV}$.