Spin rotation induced by applied pressure in the Cd-doped Ce₂RhIn₈ intermetallic compound

The pressure evolution of the magnetic properties of the Ce₂RhIn_7.79Cd_0.21 heavy fermion compound was investigated by single crystal neutron magnetic diffraction and electrical resistivity experiments under applied pressure. From the neutron magnetic diffraction data, up to P = 0.6 GPa, we found no changes in the magnetic structure or in the ordering temperature T _N = 4.8 K. However, the increase of pressure induces an interesting spin rotation of the ordered antiferromagnetic moment of Ce₂RhIn_7.79Cd_0.21 into the ab tetragonal plane. From the electrical resistivity measurements under pressure, we have mapped the evolution of T _N and the maximum of the temperature dependent electrical resistivity (T _MAX) as a function of the pressure (P ≲ 3.6 GPa). To gain some insight into the microscopic origin of the observed spin rotation as a function of pressure, we have also analyzed some macroscopic magnetic susceptibility data at ambient pressure for pure and Cd-doped Ce₂RhIn₈ using a mean-field model including tetragonal crystalline electric field (CEF). The analysis indicates that these compounds have a Kramers doublet ${\Gamma }_7^{-}$ -type ground state, followed by a ${\Gamma }_7^{+}$ first excited state at Δ₁ ∼ 80 K and a Γ₆ second excited state at Δ₂ ∼ 270 K for Ce₂RhIn₈ and Δ₂ ∼ 250 K for Ce₂RhIn_7.79Cd_0.21. The evolution of the magnetic properties of Ce₂RhIn₈ as a function of Cd doping and the rotation of the direction of the ordered moment for the Ce₂RhIn_7.79Cd_0.21 compound under pressure suggest important changes of the single ion anisotropy of Ce³⁺ induced by applying pressure and Cd doping in these systems. These changes are reflected in modifications in the CEF scheme that will ultimately affect the actual ground state of these compounds.