Switching of the magnetic order in ${\mathrm{CeRhIn}}_{5-x}$${\mathrm{Sn}}_x$ in the vicinity of its quantum critical point

We report neutron diffraction experiments performed in the tetragonal antiferromagnetic heavy fermion system ${\mathrm{CeRhIn}}_{5-x}$${\mathrm{Sn}}_x$ in its $(x,T)$ phase diagram up to the vicinity of the critical concentration $x_c$ $\approx 0.40$, where long range magnetic order is suppressed. The propagation vector of the magnetic structure is found to be ${\mathbf{k}}_{\mathbf{IC}}=(1/2,1/2,k_l)$ with $k_l$ increasing from $k_l=0.298$ to $k_l=0.410$ when $x$ increases from $x=0$ to $x=0.26$. Surprisingly, for $x=0.30$, the order has changed drastically and a commensurate antiferromagnetism with ${\mathbf{k}}_{\mathbf{C}}=(1/2,1/2,0)$ is found. This concentration is located in the proximity of the quantum critical point where superconductivity is expected.

Figure 1

$\mathbf{Q}$ scans performed along the [0,0,1] and [1,1,0] directions for ${\mathrm{CeRhIn}}_{4.84}$${\mathrm{Sn}}_{0.16}$ at $T=0.4$ K. The full lines are Gaussian fits and the dashed lines indicate the background.

Figure 2

$\mathbf{Q}$ scans performed along the [0,0,1] direction for $x=0.10$, 0.26, and 0.30 for temperatures below and above their respective Néel temperatures. The full lines are Gaussian fits.

Figure 3

Temperature dependence of a $\mathbf{Q}$ scan performed along [0,0,1] for $x=0.20$. Lines are Gaussian fits.

Figure 4

Temperature dependence of the normalized magnetic intensities, for several $x$. Lines are phenomenological fits as explained in the text.

Figure 5

Néel temperature, ordered magnetic moment, and $c$-axis component of the propagation vector. Lines are guides for the eyes.