Electronic and magnetic properties of stoichiometric CeAuBi2.

We report the electronic and magnetic properties of stoichiometric CeAuBi2 single crystals. At ambient pressure, CeAuBi2 orders antiferromagnetically below a Néel temperature (TN ) of 19 K. Neutron diffraction experiments revealed an antiferromagnetic propagation vector τ ^ = [ 0 , 0 , 1 ∕ 2 ] , which doubles the paramagnetic unit cell along the c axis. At low temperatures several metamagnetic transitions are induced by the application of fields parallel to the c axis, suggesting that the magnetic structure of CeAuBi2 changes as a function of field. At low temperatures, a linear positive magnetoresistance may indicate the presence of band crossings near the Fermi level. Finally, the application of external pressure favors the antiferromagnetic state, indicating that the 4f electrons become more localized.

Evolution of the magnetic properties in the antiferromagnet Ce2RhIn8 simultaneously doped with Cd and Ir.

We report the evolution of the magnetic properties of Ce2Rh1-xIrxIn8-yCdy single crystals. In particular, for Ce2Rh0.5Ir0.5In8 (TN=2.0K) and Ce2Rh0.5Ir0.5In7.79Cd0.21 (TN=4.2K), we have solved the magnetic structure of these compounds using single-crystal neutron magnetic diffraction experiments. Taking the magnetic structure of the Ce2RhIn8 heavy-fermion antiferromagnet as a reference, we have identified no changes in the q=12,12,0 magnetic wave vector; however, the direction of the ordered Ce3+ moments rotates toward the ab plane, under the influence of both dopants. By constraining the analysis of the crystalline electric field (CEF) with the experimental ordered moment's direction and high-temperature magnetic-susceptibility data, we have used a mean-field model with tetragonal CEF and exchange interactions to gain insight into the CEF scheme and anisotropy of the CEF ground-state wave function when Cd and Ir are introduced into Ce2RhIn8. Consistent with previous work, we find that Cd doping in Ce2RhIn8 tends to rotate the magnetic moment toward the ab plane and lower the energy of the CEF excited states' levels. Interestingly, the presence of Ir also rotates the magnetic moment towards the ab plane although its connection to the CEF overall splitting evolution for the y = 0 samples may not be straightforward. These findings may shed light on the origin of the disordered spin-glass phase on the Ir-rich side of the phase diagram and also indicate that the Ce2MIn8 compounds may not follow exactly the same Rh-Ir CEF effects trend established for the Ce2MIn5 compounds.

Tuning the crystalline electric field and magnetic anisotropy along the CeCuBi2-xSbx series.

We have performed X-ray powder diffraction, magnetization, electrical resistivity, heat capacity and inelastic neutron scattering (INS) to investigate the physical properties of the intermetallic series of compounds CeCuBi2-xSbx. These compounds crystallize in a tetragonal structure with space group P4∕nmm and present antiferromagnetic transition temperatures ranging from 3.6 K to 16 K. Remarkably, the magnetization easy axis changed along the series, which is closely related to the variations of the tetragonal crystalline electric field (CEF) parameters. This evolution was analyzed using a mean field model, which included an anisotropic nearest-neighbor interactions and the tetragonal CEF Hamiltonian. We obtained the CEF parameters by fitting the magnetic susceptibility data with the constraints given by the INS measurements. More broadly, we discuss how this CEF evolution can affect the Kondo physics and the search for a superconducting state in this family.

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

The pressure evolution of the magnetic properties of the Ce2RhIn7.79Cd0.21 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 Ce2RhIn7.79Cd0.21 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 Γ 7 - -type ground state, followed by a Γ 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 Ce2RhIn7.79Cd0.21. 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 Ce2RhIn7.79Cd0.21 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.

High-pressure studies on heavy-fermion antiferromagnet CeCuBi2.

We report in-plane electrical resistivity studies of CeCuBi2 and LaCuBi2 single crystals under applied pressure. At ambient pressure, CeCuBi2 is a c-axis Ising antiferromagnet with a transition temperature [Formula: see text] K. In a magnetic field applied along the c-axis at [Formula: see text] K a spin-flop transition takes place [Formula: see text] T. Applying pressure on CeCuBi2 suppresses T N at a slow rate. [Formula: see text] extrapolates to zero temperature at [Formula: see text] GPa. The critical field of the spin-flop transition [Formula: see text] displays a maximum of 6.8 T at [Formula: see text] GPa. At low temperatures, a zero-resistance superconducting state emerges upon the application of external pressure having a maximum T c of 7 K at 2.6 GPa in CeCuBi2. High-pressure electrical-resistivity experiments on the non-magnetic reference compound LaCuBi2 reveal also a zero resistance state with similar critical temperatures in the same pressure range as CeCuBi2. The great similarity between the superconducting properties of both materials and elemental Bi suggests a common origin of the superconductivity. We discuss that the appearance of this zero resistance state superconductivity may be related to the Bi layers present in the crystalline structure of both compounds and, therefore, could be intrinsic to CeCuBi2 and LaCuBi2, however further experiments under pressure are necessary to clarify this issue.