The 4f crystal-electric field ground state wave functions of CeRh(1-x)Ir(x)In5 have been determined by linear polarization dependent soft x-ray absorption spectroscopy (XAS) at T = 8 K. We demonstrate that these ground state wave functions correlate
with the phase diagram of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states. We discuss how certain wave functions could affect magnetic order and anisotropic hybridization, facilitating the formation of a superconducting ground state at low temperatures.
We have succeeded in establishing the crystal-field ground state of CeRu2Al10, an orthorhombic intermetallic compound recently identified as a Kondo insulator. Using polarization dependent soft x-ray absorption spectroscopy at the Ce M4,5 edges, toge
ther with input from inelastic neutron and magnetic susceptibility experiments, we were able to determine unambiguously the orbital occupation of the 4f shell and to explain quantitatively both the measured magnetic moment along the easy a axis and the small ordered moment along the c-axis. The results provide not only a platform for a realistic modeling of the spin and charge gap of CeRu2Al10, but demonstrate also the potential of soft x-ray absorption spectroscopy to obtain information not easily accessible by neutron techniques for the study of Kondo insulators in general.
We have successfully determined the hitherto unknown sign of the B44 Stevens crystal-field parameter of the tetragonal heavy-fermion compound CeCu2Si2 using vector q dependent non-resonant inelastic x-ray scattering (NIXS) experiments at the cerium N
4,5 edge. The observed difference between the two different directions q||[100] and q||[110] is due to the anisotropy of the crystal-field ground state in the (001) plane and is observable only because of the utilization of higher than dipole transitions possible in NIXS. This approach allows us to go beyond the specific limitations of dc magnetic susceptibility, inelastic neutron scattering, and soft x-ray spectroscopy, and provides us with a reliable information about the orbital state of the 4f electrons relevant for the quantitative modeling of the quasi-particles and their interactions in heavy-fermion systems.
Soft x-ray absorption experiments on the transition metal L2,3 edge of multiferroic MnWO4 and antiferromagnetic CoWO4 are presented. The observed linear polarization dependence, analyzed by full-multiplet calculations, is used to determine the ground
state wave function of the magnetic Mn2+ and Co2+ ions. The impact of the local structure and the spin-orbit coupling on the orbital moment is discussed in terms of the single-ion anisotropy. It is shown that the orbital moment in CoWO4 is responsible for the collinear antiferromagnetism, while the small size of spin-orbit coupling effects make spiral magnetic order in MnWO4 possible, enabling the material to be multiferroic.
