AVS 68 Session AC+LS+MI-WeM: Magnetism, Electron Correlation, and Superconductivity in the Actinides/Rare Earths

Wednesday, November 9, 2022 8:00 AM in Room 318

Wednesday Morning

Session Abstract Book
(293KB, Nov 18, 2022)
Time Period WeM Sessions | Abstract Timeline | Topic AC Sessions | Time Periods | Topics | AVS 68 Schedule

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8:00 AM AC+LS+MI-WeM-1 The Relation between Crystal Chemistry and Superconductivity in Actinide-Based Superconductors
Eteri Svanidze (Max Plank Institute, Dresden, Germany)

Crystallographic features play an important role in the physical and chemical properties of a given solid-state material. In particular, actinide-based systems exhibit a wide range of properties – from unconventional superconductivity to peculiar magnetic orders. In this talk, I will highlight some of the old and new actinide-based superconductors, in which a delicate interplay between chemistry and physics is observed. A comprehensive characterization of properties of UBe13 has revealed a deep interrelation between the physical and chemical features. Notably, single crystals of this material tend of include many defects which have a dramatic effect on superconducting state [1]. Motivated by this issue, an alternative method of studying intrinsic properties is investigated [2-4]. By creating a micro-scale device, it is possible to measure intrinsic superconductivity of UBe13, whichhas so far remained out of reach [4]. The properties of UBe13 are compare to those of other actinide-based superconductors – UTe2 [5] and Th4Be33Pt16 [6] – in which a strong coupling of lattice and superconducting properties is observed. By studying these systems, it is possible to expand the understanding of crystal chemistry of solid-state materials, while simultaneously providing an insight into which crystallographic parameters impact the physical properties of a given solid-state material.

[1] A. Amon et al., “Tracking aluminium impurities in single crystals of the heavy-fermion superconductor UBe13,”Sci. Rep.8, 10654 (2018)

[2] E. Svanidze et al., “Revealing intrinsic properties of UBe13”, in preparation (2022)

[3] A. Amon et al., "Interplay of atomic interactions in the intermetallic semiconductor Be5Pt", Angew. Chem. Int. Ed.58, 2 (2019).

[4] I. Antonyshyn et al., "Micro-scale device - an alternative route for studying the intrinsic properties of solid-state materials: case of semiconducting TaGeIr", Angew. Chem. Int. Ed.59, 2 (2020)

[5] E. Svanidze et al., “Intrinsic crystal structure of UTe2”, in preparation (2022)

[6] P. Kozelj et al., “A noncentrosymmetric cage superconductor Th4Be33Pt16”, Sci. Rep.11, 22352 (2021)

8:40 AM AC+LS+MI-WeM-3 Revealing The Beauty of Uranium Compounds:the UMB4 (M=V, Cr, Fe, Co, Mo, W, Re, Os) and UFexSb2 Cases
Antonio Pereira Gonçalves (Instituto Superior Técnico, Univ. Lisboa)

Uranium-based phases with d-metals show a vast and rich variety of physical properties, some of them unique, which are mainly driven by the large 5f spin-orbit coupling and the degree of delocalization of the 5f states. The understanding of such behaviors is critical for the advance of Solid State Sciences and can lead to the discovery of new phenomena and ground states. In this talk, examples of uranium compounds with unusual properties are presented, the focus being on UMB4 materials and UFexSb2 alloys.

UMB4 (M=V, Cr, Fe, Co, Mo, W, Re, Os) compounds are quite notable, crystallizing in the YCrB4-type (for V, Cr, Fe, Co) and ThMoB4 type (for Mo, W, Re, Os) polymorphs. Both structures are closely related, containing the same number of atoms in the unit cell and similar coordination polyhedral, which allows the comparison of their properties as a function of the d-metal. Their electronic structure is influenced by a strong hybridization between the B-2p states and both the d-metals d-states and the uranium (5f) valence band states. This avoids the formation of narrow bands with high density of states at the Fermi level, even if the 5f-d hybridization is weak, i.e. for late d-metals. Hence, the explored UMB4 compounds are weak Pauli paramagnets, with a density of states at Fermi level of only ~4 times higher than for α-U. Those crystalizing in the ThMoB4 structure show anomalous lattice vibrations, in particular the presence of low-energy Einstein modes, which can lead to superconducting ground states.

UFexSb2 alloys crystallize in the HfCuSi2 type structure and present a remarkable ground state evolution with Fe concentration. UFe0.5Sb2 shows a non-Fermi liquid behavior, with a change from metallic to semiconductor-upon applying magnetic field. In contrast, UFe0.7Sb2 (and, in a minor scale, UFeSb2), shows an increase in electrical resistivity with decreasing temperature under zero magnetic field, but for high magnetic fields a metallic behavior is established. First principles calculations indicated that in UFeSb2 some bands cross the Fermi level, but they are relatively steep and, as a result, the density of states at Fermi level is low, which supports the semi-metallic character of this composition. In the case of UFe0.5Sb2, a higher concentration of bands at the Fermi level, some of them relatively flat, exist, which cause a sudden step-shaped drop of density of states just above Fermi level. The magnetic field application can raise the Fermi level into the pseudo-gap, which is probably the reason for the change from a metallic-like to a semiconductor-like behavior.

10:00 AM BREAK - Complimentary Coffee in Exhibit Hall
11:00 AM AC+LS+MI-WeM-10 Uranium Hydrides Revisited
Ladislav Havela (Charles University, Faculty of Mathematics and Physics); Dominik Legut (VSB Technical University Ostrava); Jindrich Kolorenc (Institute of Physics, Czech Academy of Sciences)

Uranium hydrides are not only materials important for understanding of fundamental aspects of actinides. They are also relevant for nuclear technologies as well as for specific hydrogen storage tasks, as e.g. storing of tritium in nuclear fusion devices. Electronic structure of uranium hydrides (α- and β-UH3, UH2) reflects two contradictory tendencies. One is a charge transfer from U towards H, the other is a stability of the f shell. The latter is illustrated also on the case of rare earth hydrides with anomalous rare earth elements, such as Yb or Eu, which surprisingly retain their lower valence state, i.e. with a higher f-occupancy. The transfer is thus realized in U by the 6d and 7s electrons, which become noticeably depleted, but the 5f occupancies remain high. The concomitant reduction of the 5f-6d hybridization contributes, together with the volume expansion, to pronounced ferromagnetism of the U hydrides with Curie temperatures far above 100 K. We compare individual hydrides described by the GGA+U calculations, yielding numbers on the charge transfer or spin and orbital moments, with relevant experimental data. Interesting feature obtained from calculations is that the two different U sites in β-UH3 have the respective magnetizations non-collinear. The same calculations yield also phonon dispersion relations, which are used to determine the temperature dependence of phonon contribution to heat capacity. The agreement in the paramagnetic range is so good that it allows to determine both the magnetic entropy and changes of the Sommerfeld coefficient between the ground state and paramagnetic state, the latter being twice higher. The position of the U hydrides on the map of localization-delocalization dichotomy will be discussed.

The work was supported by the Czech Science Foundation under the grant No. 21-09766S.

11:20 AM AC+LS+MI-WeM-11 Towards a Better Understanding of the Rkky Interaction in Ce- and Yb-Based Compounds: Anisotropies from Cef Effects and Fermi Surfaces
Gertrud Zwicknagel (Institut für Mathematische Physik); Vilen Zevin (The Racah Institute of Physics)

We calculate the influence of Crystalline Electric Field (CEF) effects and the Fermi surface topology on the indirect Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction between local 4f moments in Ce- and Yb-compounds. Starting from a periodic Anderson model, we show that the anisotropy of the CEF ground state manifests itself in the anisotropy of the effective exchange coupling constant J(R,R’) between two moments at sites R and R’. If spin-orbit effects among the conduction states can be neglected, the interaction between two Kramers doublets is isotropic in pseudo-spin space. Adopting the Stationary Phase approach, we derive the asymptotic form of the exchange constant for arbitrary Fermi surfaces. We evaluate the anisotropy of the RKKY interaction in tetragonal Ce- and Yb-122 compounds for realistic model bands. The influence of spin-orbit interaction among the conduction electrons is discussed.

11:40 AM AC+LS+MI-WeM-12 Mechanically Forced Tuning of Interactions in Tetragonal 221 Intermetallics
Petr Král, Jiří Prchal (Charles University, Czech Republic); Jiří Kaštil (Czech Academy of Sciences, Czech Republic); Dominik Daisenberger (Diamond Light Source, UK); Daniel Staško (Charles University, Czech Republic)

Family of R2T2X intermetallics adopting the tetragonal Mo2FeB2-type crystal structure represents the group of anisotropic systems with potential to exhibit geometrical frustration effects due to the Shastry-Sutherland-like arrangement of R-atoms in the aa-planes alternated by usually non-magnetic T-X planes along the crystallographic c-axis. Crucial for resulting magnetic behavior are the interatomic distances affecting the exchange interactions between individual ions. Especially interesting may be the compounds close to the empirical boundary of crystal structure stability since, based on available data, the lowest observed unit-cell volume among Mo2FeB2-type materials is about Vf.u.,crit = 200 Å3.

The unique tool allowing to act directly on the interatomic distances without changes of chemical composition is mechanical pressure. Employing the high-pressure techniques, it is possible to influence all lattice-related physical properties including e.g. the magnetic interactions and electronic structure. Especially in the strongly anisotropic compounds, the hydrostatic pressure effect depends on the compressibility of individual lattice parameters. This is the case, when the uniaxial pressure may represent the opportunity to act selectively in chosen crystallographic directions and thus to provide the insight into the layout of interactions within the crystal lattice.

Herewith, we are presenting the results of systematical study of pressure impact on the R2T2X compounds. Special attention is paid to Ce2Pd2In considered to be one of the most interesting systems among R2T2X family. It represents the rare example of Ce-based ferromagnet, however the ground state is reached through the antiferromagnetic interphase. High sensitivity of magnetic behavior to hydrostatic pressure has been revealed showing the preference of antiferromagnetic phase at lower pressures followed by the Kondo-like anomaly formation and suppression of magnetic ordering at pressures around 4 GPa. Based on the results of high-pressure XRD experiment, the hydrostatic pressure acts more significantly within the basal plane. Indeed, different response to the uniaxial pressure applied along the c-axis was observed.

Compounds with the unit-cell volume closest to Vf.u.,crit belongs to the series R2Cu2In. Among them the ferromagnets Dy2Cu2In (exhibiting the signs of spin-reorientation at lower temperatures) and Tm2Cu2In (with signs of spin-glass behavior) were investigated. Concerning the later one, the pressure was found to support the frustration effects responsible for the spin-glass properties as the unit-cell volume tends to reach the Vf.u.,crit.

12:00 PM AC+LS+MI-WeM-13 Effects of O2 Growth Pressure on the Magnetization of LaMnO3-SrTiO3 Thin Films
Ghadendra Bhandari (West Virginia University); Robbyn Trappen (University of Waterloo); Navid Mottaghi, Mikel Barry Holcomb (West Virginia University)

Magnetic properties of epitaxial LaMnO3 thin films grown on SrTiO3 substrate have been studied. Thin films are grown at various oxygen pressure using pulsed laser deposition and deposition has been monitored by reflection high energy electron diffraction (RHEED) to verify layer-by-layer growth. Bulk stoichiometric LaMnO3 exhibits A-type antiferromagnetic order, whereas thin films show a ferromagnetic FM phase. Structure and magnetic properties have been characterized by X-ray diffractometry (XRD), X-ray reflectivity (XRR) and vibration sample magnetometry (VSM). The thin films are showing ferromagnetic (FM) phase. Depth dependent magnetization studied by polarized neutron beam reflectivity found that magnetization is higher near interfacial region and a magnetically dead region lies at the surface. We have observed c-lattice correlated magnetization, which is minimized at 30mTorr O2 pressure.

Session Abstract Book
(293KB, Nov 18, 2022)
Time Period WeM Sessions | Abstract Timeline | Topic AC Sessions | Time Periods | Topics | AVS 68 Schedule