Rare Earth Metallic Systems Research Articles

Non-Fermi liquid behavior and quantum criticality in cubic heavy fermion systems with non-Kramers multipolar local moments

Notable non-Fermi liquid and quantum critical behaviors are observed in rare-earth metallic systems with non-Kramers local moments supporting a number of different multipolar moments. A prominent example is $\text{Pr(Ti,V)}_{2}\text{Al}_{20}$, where the non-Kramers doublet of the $\text{Pr}^{3+}$ ion allows quadrupolar and octupolar moments, but lacks a dipolar moment. Previous theoretical studies show that a single impurity Kondo problem with such an unusual local moment leads to novel non-Fermi liquid states. In this work, we investigate possible quantum critical behaviors arising from the competition between non-Fermi liquid states and multipolar-ordered phases induced by the RKKY interaction. We consider a local version of the corresponding Kondo lattice model, namely the Bose-Fermi Kondo model. Here, the multipolar local moments are coupled to fermionic and bosonic bath degrees of freedom representing the multipolar Kondo effect and RKKY interactions. Using a perturbative renormalization group (RG) study up to two loop order, we find critical points between non-Fermi liquid Kondo fixed points and a quadrupolar ordered fixed point. The critical points describe quantum critical behaviors at the corresponding phase transitions and can be distinguished by higher order corrections in the octupolar susceptibility that can be measured by ultrasound experiments. Our results imply the existence of a rich expansion of the phases and quantum critical behaviors in multipolar heavy fermion systems.

Critical Theory of Non-Fermi Liquid Fixed Point in Multipolar Kondo Problem

When the ground state of a localized ion is a non-Kramers doublet, such localized ions may carry multipolar moments. For example, Pr$^{3+}$ ions in a cubic environment would possess quadrupolar and octupolar, but no magnetic dipole, moments. When such multipolar moments are placed in a metallic host, unusual interactions between these local moments and conduction electrons arise, in contrast to the familiar magnetic dipole interactions in the classic Kondo problem. In this work, we consider the interaction between a single quadrupolar-octupolar local moment and conduction electrons with $p$-orbital symmetry as a concrete model for the multipolar Kondo problem. We show that this model can be written most naturally in the spin-orbital entangled basis of conduction electrons. Using this basis, the perturbative renormalization group (RG) fixed points are readily identified. There are two kinds of fixed points, one for the two-channel Kondo and the other for a novel fixed point. We investigate the nature of the novel fixed point non-perturbatively using non-abelian bosonization, current algebra and conformal field theory approaches. It is shown that the novel fixed point leads to a, previously unidentified, non-Fermi liquid state with entangled spin and orbital degrees of freedom, which shows resistivity $\rho \sim T^{\Delta}$ and diverging specific heat coefficient $C/T \sim T^{-1 + 2\Delta}$ with $\Delta=1/5$. Our results open up the possibility of myriads of non-Fermi liquid states, depending on the choices of multipolar moments and conduction electron orbitals, which would be relevant for many rare-earth metallic systems.

Physicochemical Interaction in Systems Formed by Trivalent REM with Group IV p-Elements. IV. Phase Thermodynamics

The available data are analyzed on the enthalpies of formation of intermetallic compounds in binary systems of rare-earth metals with group IV p-elements. Consideration is given to effects of metallochemical factors on these enthalpies of formation. For REM silicides and germanides, the dominant effect comes from the size factor, while for the plumbides, it comes from the electronegativity. The effects of these factors tend to balance for compounds containing tin.

Magnetic dichroism in valence-band x-ray photoemission spectroscopy

The availability of tunable synchrotron radiation of well defined polarization allowed it to refine more or less all kind of electronic spectroscopies during the last years [1]. In particular detailed information on magnetic solids [1] could be obtained by investigating the various types of spin-orbit induced magnetic dichroism. In the case of core level photo emission spectroscopy magnetic dichroism could be observed for transition metal as well as rare earth metal systems by using circularly [2], linearly [3] and even unpolarized [4] radiation in a spin-integrated as well as spin-resolved way. A corresponding theoretical description has been developed by various authors starting from an itinerant [5] or atomic description [6] of the underlying electronic structure. The linear and circular forms of magnetic dichroism in valence band (VB) photoemission has been investigated experimentally by several groups [7] in the UV regime. A proper theoretical description of these experiments on transition metal systems could be given by Feder and coworkers [8] by extending the one-step model of photo emission to the spin-polarized relativistic situation. These investigations done with polarized radiation give an extremely detailed insight into the electronic structure of the investigated material because of the various selection rules. For the X-ray regime, however, the k-selection rule is no more present [9]. Nevertheless, as will be demonstrated below, a pronounced magnetic dichroism still occurs in that case — even for angular integrated spectra.

The thermodynamic properties of rare earth metallic systems

The enthalpies of formation of intermetallic compounds based on rare earth elements have been gathered in this paper. We have focused our attention on the data obtained using calorimetric methods. The rare earths exhibit strong interactions with metallic elements, Be and Mg, the late transition metals and with the elements of groups IB to VB. The experimental values of the enthalpies of formation of rare-earth-based alloys have been compared with estimations of these values using semi empirical formulation and tight-binding approximation.

Erratum: Modulated Magnetic Phases in Rare Earth Metallic Systems

The numbers in the y -axis of figure 2 (p. 227) in the article "Modulated magnetic phases in rare earth metallic systems" by T. Chattopadhyay (8 Apr., p. 226) were incorrect. They should have been 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, and 0.28, respectively.

Modulated Magnetic Phases in Rare Earth Metallic Systems

Neutron scattering has played a key role in the microscopic understanding of the static and dynamic properties of magnetic materials. Modulated magnetic structures first discovered in the late fifties can no longer be referred to as exotic; more than a hundred such phases have already been found in a variety of magnetic systems. Neutron and x-ray magnetic scattering have played a complementary role in the recent discovery and understanding of the modulated magnetic phases in rare earth metallic systems.

Model calculation of the static magnetic susceptibility in light rare earth metallic systems

Model calculation of the static magnetic susceptibility in light rare earth metallic systems

Evidence in rare-earth (R)–transition metal (M) intermetallics for a systematic dependence of R-M exchange interactions on the nature of the R atom

In rare earth (R)–transition metal (M) compounds, large R-M magnetic interactions can occur, which give rise to higher values of the ordering temperature (TC,TN) for compounds with magnetic R elements than for compounds with R nonmagnetic, i.e., La, Lu, Y. Due to the localized character of the 4f shell, these R-M interactions are indirect, mediated by the 5d, 6s conduction electrons. The highest value of the ordering temperature is obtained for Gd compounds, and as a first approximation it is reasonable to write the interaction energy as ER-M=−nRMMSRMSM, where MSR and MSM are the rare-earth and transition metal spin moments, respectively. The molecular field coefficient nRM is generally assumed to be a constant throughout a given series, owing to the similarities of band structure for all R elements. In this paper, the molecular field coefficient nRM has been obtained for a number of series of rare earth-transition metal compounds. The analysis reveals that nRM is not a constant going across a given series but decreases by a factor of 2. The observed variation in nRM is shown to be related to the variation of the exchange interactions between 4f and 5d electrons which are larger for light rare-earth elements since the difference between the spatial extent of the 4f and 5d electrons is reduced. As a general rule the observed enhancement of magnetic interactions for lightest rare earths in all rare-earth metallic systems can be attributed to the same phenomenon.

A model for electrons existing in hybridized narrow and wide bands

We propose a model for electrons existing in hybridized narrow and wide bands which occur in the transition metals, the mixed valence systems of rare earth metals and their compounds, and the doped semiconductors, etc. The model is derived from the standard basis operator (SBO) form of the extended Anderson model, originally proposed for the dilute magnetic alloys. The equation of motion method has been used to obtain the SBO's Green's functions and, thereby, the spectrum of the quasi-particle excitations. For translationally invariant systems, we found the possibility of the nonmetallic behavior and the metal-nonmetal transition for a nonintegral number of electrons per lattice site.

The hydrolysis of rare earth carbides

The hydrolysis products of some rare earth carbides, oxycarbides and nitride-carbides have been studied. With hydrolysis under gentle conditions, product distributions are simple and consistently reproducible, and are representative of the carbon species in the lattice. Consideration of the surface chemistry of the hydrolysis reaction is important in interpretation of results. The use of the hydrolysis reaction to study the nature of the carbon species in carbon-containing phases of several binary and ternary rare earth metal systems is outlined.