Anisotropy of critical correlations in moderately delocalized cerium and actinide systems

The equilibrium and excitation magnetic behavior of a class of cerium and light actinide compounds have been explained previously, in a theory first developed by Siemann and Cooper, in terms of a band-f-electron anisotropic hybridization-mediated two-ion interaction of the Coqblin- Schrieffer type. Using the same theory, we present here a calculation, within the random-phase approximation, of the longitudinal component of the static wave-vector-dependent susceptibility in the paramagnetic phase. The calculations have been performed in the presence of a cubic crystal field (CF) and yield results for the ratio of inverse critical correlation lengths, K||/K_, parallel and perpendicular to the moment direction, that compare well with those of diffuse critical neutron scattering experiments. In Ce3+ (f1) compounds, we find that as the CF interaction (F7 ground state) predominates over the two-ion interaction, the relative strength of the coupling within the ferromagnetic [001] planes (with moments perpendicular to the planes) and that between the [001] planes is gradually reversed, resulting in a ratio K||/K_ smaller than unity, as is experimentally observed. We also present results for the effect of differing intraionic (L-S,intermediate, and j-j) coupling on K||/K_ for the case of Pu3+(f5) and U3+(f3) compounds

Magnetic instability with increasing hybridization in cerium compounds

A synthesis of a phenomenological theory of orbitally driven magnetic ordering of moderately delocalized light rare-earth systems and ab initio electronic structure calculations has been applied to investigate the change in magnetic behavior on going from CeSb to CeTe, both of which have rocksalt structure with a small decrease in lattice parameter. The hybridization-potential matrix elements and the band energies entering the Anderson-lattice Hamiltonian are obtained from linear-muffin-tin-orbital (LMTO) electronic-structure calculations with the Ce 4f states treated as core states. The position of the Ce 4f energy level relative to the Fermi energy and the intra-atomic Coulomb energy U are obtained by use of a sequence of three total-energy supercell calculations with one out of four Ce sites constrained to f occupation with n=0, 1,2, successively. The calculations elucidate the origins, in the electronic structure, of the variation of the f-state resonance width and hybridization potential on going from Cesb to CeTe, and the resultant sensitivity of the hybridization dressing of the crystal-field splitting and the hybridization-induced exchange interactions to chemical environment. The effect of opening up successive angular momentum scattering channels of the ab initio calculated two-ion exchange-interaction matrix on the nature of the magnetic ordering is examined. The calculated magnitude and range dependence of the two-ion exchange interactions changes sharply from CeSb to CeTe, yielding a change in magnetic behavior in qualitative agreement with experiment. The nonlinear hybridization effects on the hybridization dressing of the crystal-field splitting have been examined. These effects, which are associated with the self-consistent determination of both the band states and f states in the presence of band-f hybridization, are found to be small in both systems

Hybridization-induced magnetism in correlated cerium systems

There is a great change in the nature of the magnetic ordering on going from CeIn3, a local moment antiferromagnetic system, to CePb3, a heavy fermion itinerant antiferromagnetic system, both of which have Cu3Au crystal structure. We have applied ab initio electronic structure calculations, based on the linear-muffin-tin-orbital method, and a phenomenological theory of orbitally driven magnetic ordering, to study the effects of the band-f hybridization-induced interactions and the band-f exchange-induced interactions, pertinent to the magnetic behavior of these systems. The position of the Ce 4 f energy level relative to the Fermi energy and the intra-atomic Coulomb interaction are obtained from a sequence of three total-energy supercell calculations with two, one and zero f electrons in the Ce 4 f core. The calculations elucidate the origins in the electronic structure of the variation of the f-state resonance width characterizing the strength of the hybridization and the density of states at the Fermi energy characterizing the number and character of band states available for hybridization. We present results for the hybridization potential and the hybridization-induced exchange interactions on going from CeIn3 to CePb3, where the only obvious change is the addition of an anion p electron

Resonant band-electron –f -electron scattering theory for highly correlated actinide systems

In earlier studies we recognized that the highly correlated behavior of the f electrons within moderately delocalized light actinide (uranium, neptunium, plutonium) systems is linked to the non-f-band behavior via the hybridization process. By transforming the hybridization into a bandelectron-f-electron resonant scattering from the correlated multiplet states of the actinide ions, and considering only the scattering processes that involve f electrons in the ml=0, ms=+/-1/2 states (for quantization along the interionic axis) which dominate the two-ion interactions, our earlier work explained the main features of the anisotropic magnetic equilibrium behavior for the PuSb system but failed to reproduce the correct polarization (longitudinal) for the long-period antiferromagnetic structure observed in the temperature range below the Neel temperature. In this paper we include the next-to-dominant scattering channels (single-site scattering processes involving f electrons with ml=+/-1, ms-/+1/2). This refinement changes the angular dependence of the anisotropic interaction, and successfully yields the ferromagnetic to longitudinally polarized long-period antiferromagnetic phase transition as is experimentally observed. Excellent agreement with experiment for the correlation length anisotropy is also obtained. For the magnetic excitation behavior in the ferromagnetic phase pertinent to PuSb at T=O, the theory gives a spectrum with two polarized branches at the zone boundary for q along the [100] (transverse-to-moment) direction. In fact, the predicted excitation behavior is rather remarkable. The appearance of two polarized branches rather than a single branch at the zone boundary occurs only over an extremely narrow range of crystal-field splitting. We choose the crystal-field splitting to give two branches, and this unadjustably yields excitation energies that are very close to the experimental values. An only slightly different crystal-field value would give neither two branches nor correct excitation energies

Strongly Correlated Cerium Systems: Non-Kondo Mechanism for Moment Collapse

We present an ab initio based method which gives clear insight into the interplay between the hybridization, the coulomb exchange, and the crystal-field interactions, as the degree of 4f localization is varied across a series of strongly correlated cerium systems. The results for the ordered magnetic moments, magnetic structure, and ordering temperatures are in excellent agreement with experiment, including the occurence of a moment collapse of non-Kondo origin. In contrast, standard ab initio density functional calculations fail to predict, even qualitatively, the trend of the unusual magentic properties.Comment: A shorter version of this has been submitted to PR

Proprioception and Tension Receptors in Crab Limbs: Student Laboratory Exercises

The primary purpose of these procedures is to demonstrate for teaching and research purposes how to record the activity of living primary sensory neurons responsible for proprioception as they are detecting joint position and movement, and muscle tension. Electrical activity from crustacean proprioceptors and tension receptors is recorded by basic neurophysiological instrumentation, and a transducer is used to simultaneously measure force that is generated by stimulating a motor nerve. In addition, we demonstrate how to stain the neurons for a quick assessment of their anatomical arrangement or for permanent fixation. Staining reveals anatomical organization that is representative of chordotonal organs in most crustaceans. Comparing the tension nerve responses to the proprioceptive responses is an effective teaching tool in determining how these sensory neurons are defined functionally and how the anatomy is correlated to the function. Three staining techniques are presented allowing researchers and instructors to choose a method that is ideal for their laboratory