Valence transitions and intermediate valence states in rare earth and actinide materials

A non-interacting local Fermi liquid theory applicable to Ce, Sm, Eu and Yb metallic intermediate valence materials is presented. The induced density of states of a given rare earth ion is taken as the Lorentzian appropriate for a rare earth ion impurity, for which the justification is tentatively discussed. The degeneracy of the resonance is that of the magnetic configuration of the ion. The results are applied to the f occupation, susceptibility and specific heat. A relationship existing in the literature between the zero temperature susceptibility and linear coefficient of specific heat follows exactly from the present very simple theory. The results are compared with a range of experimental data.

https://iopscience.iop.org/article/10.1088/0305-4608/10/11/016/pdf

A local Fermi liquid theory of intermediate valence systems

Approximate treatments of intermediate valence and heavy fermion model systems

The electrical resistivity of CePd3, La1−xCexPd3, CeRhxPd3−x and Ce Pd3+x systems has been measured from helium temperature to 300 K. The resistivity of pure CePd3 rises from 125 μ Ω cm to 150 μ Ω cm as one cools from 300 K to 100 K. Below 100 K the resisitivity drops dramatically to 10 μ Ω cm at low temperatures. The same qualitative behavior, though less pronounced, is observed in other systems such as CeSn3 which like CePd3 are believed to be of intermediate valence. For x<0.3 the system La1−xCexPd3 is believed to be trivalent. We observe Kondo‐like behavior in this regime. For x near unity we observe that extremely small amounts of La eliminate the rapid fall in resistivity observed below 100 K for pure CePd3. These results suggest that this fall off is due to some type of cooperative Ce ion hehavior. The CeRhxPd3−x system allows one to monitor the effect on resistivity of varying the Ce valence from 3.45 in CePd3 to 4 in CeRh.64Pd2.36. We find that the magnitude of the resistivity rise (upon cooling from 300 K to low temperature) decreases as the Ce valence increases towards four.

Resistive behavior and intermediate valence effects in La1−xCexPd3 and CePd3−xRhx

The specific heat, dc magnetization, and resistivity have been measured on a number of samples of CeCu2Si2, which was previously found to assume a novel superconducting state below 0.5 K [F. Steglich et al., Phys. Rev. Lett. 43, 1892 (1979)]. By comparing the transition temperatures of samples which have undergone different heat treatments, we demonstrate that small fractions of spurious phases hinder the onset of superconductivity but are gradually removed with annealing. With a very pure sample obtained in this way, we have fully confirmed all the characteristics of the superconducting phase transition reported before on less pure samples. However, even after this heat treatment, the samples show clear signs of striking inhomogeneities, manifested by a static Meissner effect of bulk samples representing typically only a few percent of the volume. An increase of this Meissner signal up to 60 vol% is observed after powdering the samples. In addition to measurements in the superconducting state, the intrin...

Superconductivity in CeCu2Si2 (invited)

Diffuse neutron scattering on the intermediate valence compound CePd/sub 3/ shows a quasi-elastic line with Lorentzian shape and very large, nearly temperature-independent width (GAMMA/2 approx. = 20 meV). The intensity under this line has 4f form factor but the total cross section indicates only 0.5 4f electron per formula unit. These observations are interpreted by spontaneous relaxation of the local 4f magnetization due to interconfiguration fluctuation between 4f/sup 1/ and 4f/sup 0/.

Spontaneous relaxation of the local 4f magnetization in CePd/sub 3/

We performed diffuse neutron scattering measurements with TOF-analysis at several angles in the temperature interval 3.5–300 K. Our results indicate magnetic scattering, which is consistent with a 4f-form factor and a fractional occupation of about 0.5 electron in the 4f-shell. The magnetic quasielastic line is broadened to a nearly temperature independent width of about 19 meV.

M. Loewenhaupt

Papers

Spontaneous relaxation of the local 4f magnetization in CePd/sub 3/

Temperature dependence of the magnetic neutron scattering cross section and of the line width for CePd3