Evolution of magnetism in simultaneously Cd and Ir doped heavy fermion Ce2RhIn8

The Ce$M$In$_5$ ($M$ = Co, Rh, Ir) family has been relentlessly studied owing to its complex phase diagram, an outcome of the competition between the Ruderman–Kittel–Kasuya–Yosida interaction, Kondo and crystalline electric field (CEF) effects [1]. The latter is heavily tuned by the system’s dimensionality. Therefore, following the changes of the crystal field in a system with a fundamentally different dimensionality, such as the Ce$_2M$In$_8$ ($M$ = Rh, Ir), could be key to comprehending their role on the emergence of exotic phenomena. Lately, plenty of evidence came to light that the orbital contribution and symmetry properties of the CEF ground state wavefunction of Ce ions may ultimately determine the main physical properties of these Ce-based families [2,3]. The magnetic structure (in particular the ordered moment’s direction) can provide valuable information about the system’s CEF through single ion anisotropy. However, the magnetic structure of the Ce$_2$Rh$_{1-x}$Ir$_x$In$_{8-y}$Cd$_y$ alloys and their CEF scheme remain to be explored in greater detail.
The physical properties of the Ce$_2$Rh$_{1-x}$Ir$_x$In$_8$ series and the effects of Cd substitution in Ce$_2M$In$_8$ have been previously investigated [4,5]. It has been shown that Ir doping apparently suppresses the antiferromagnetic (AFM) state and induces a superconducting and a spin-glass phase in the Ir-rich compounds. This evolution sees an increase of hybridization and hints at modifications in the CEF scheme. Cd doping, contrarily, favors AFM for $M$ = Rh and suppresses superconductivity for $M$ = Ir. Similar to the Ce$M$In$_5$ compounds, Cd in these systems seems to mainly perform electronic tuning of the ground state [6,7,8].
In this work, we performed neutron magnetic diffraction in pure and Cd doped Ce$_2$Rh$_{0.5}$Ir$_{0.5}$In$_{8-y}$Cd$_y$ ($T_N$ = 2.0 K, $y$ = 0 and $T_N$ = 4.2 K, $y$ = 0.21) and discuss the physical properties of other Ce$_2$Rh$_{1-x}$Ir$_x$In$_{8-y}$Cd$_y$ alloys. By constraining the investigation of the CEF effects with the moment’s direction, we analyzed high-temperature magnetic anisotropy using a mean field model with tetragonal CEF and exchange interactions. In accordance with previous results, the presence of Cd leads the magnetic moment to rotate toward the ab-plane and lower the energy of the excited CEF states. Ir-doping seems to increase the CEF levels’ separation and hybridization, notably rotating the moment to the basal plane as well. These studies enabled us to propose crystal field schemes and some general trends over the separation of crystal field levels, shedding light over the origin of the disordered state in Ir-rich compounds and suggesting that the Ce$_2M$In$_8$ compounds may not follow the same Rh-Ir trend as the Ce$M$In$_5$ compounds.

[1] P. G. Pagliuso et al, J. Appl. Phys. \textbf{99}, 08P703 (2006).
[2] T. Willers et al, Phys. Rev. B, \textbf{81} 195114 (2010).
[3] T. Willers, et al, PNAS USA, \textbf{112}, vol. 8, p. 2384-2388 (2015).
[4] E. N. Hering et al, Phys. Rev. B, \textbf{82}, 184517 (2010).
[5] C. Adriano et al, Phys. Rev. B \textbf{81}, 245115 (2010).
[6] R. R. Urbano et al, Phys. Rev. Lett., \textbf{99} (14) 146402 (2007).
[7] S. Seo et al, Nat. Phys. \textbf{10}, 120–125 (2014).
[8] K. Chen et al, Phys. Rev. B, \textbf{97},045134 (2018).