Monika Gamza

Electronic correlations inFeGa3 and the effect of hole doping on its magnetic properties

We investigate signatures of electronic correlations in the narrow-gap semiconductor FeGa 3 by means of electrical resistivity and thermodynamic measurements performed on single crystals of FeGa 3 , Fe 1−x Mn x Ga 3 , and FeGa 3−y Zn y , complemented by a study of the 4d analog material RuGa 3 . We find that the inclusion of sizable amounts of Mn and Zn dopants into FeGa 3 does not induce an insulator-to-metal transition. Our study indicates that both substitution of Zn onto the Ga site and replacement of Fe by Mn introduces states into the semiconducting gap that remain localized even at highest doping levels. Most importantly, using neutron powder diffraction measurements, we establish that FeGa 3 orders magnetically above room temperature in a complex structure, which is almost unaffected by the doping with Mn and Zn. Using realistic many-body calculations within the framework of dynamical mean field theory (DMFT), we argue that while the iron atoms in FeGa 3 are dominantly in an S=1 state, there are strong charge and spin fluctuations on short-time scales, which are independent of temperature. Further, the low magnitude of local contributions to the spin susceptibility advocates an itinerant mechanism for the spin response in FeGa 3 . Our joint experimental and theoretical investigations classify FeGa 3 as a correlated band insulator with only small dynamical correlation effects, in which nonlocal exchange interactions are responsible for the spin gap of 0.4 eV and the antiferromagnetic order. We show that hole doping of FeGa 3 leads, within DMFT, to a notable strengthening of many-body renormalizations.

Electronic structure and thermodynamic properties of Ce3Rh4Sn13 and La3Rh4Sn13

We report on the electronic structure and basic thermodynamic properties of Ce3Rh4Sn13 and of the reference compound La3Rh4Sn13. XPS core-level spectra revealed a stable trivalent configuration of the Ce atoms in Ce3Rh4Sn13, consistent with magnetic susceptibility data. Band structure calculations within the LSDA+U approximation yield the qualitatively correct description of Ce in a trivalent state. The reliability of the theoretical results has been confirmed by a comparison of the calculated XPS valence band spectra with experimental data. The calculated densities of states as well as the rare-earth (RE) 3d XPS spectra point to a weak hybridization between the RE 4f shell and the conduction band states. The band structure calculations result in a magnetic ground state for Ce3Rh4Sn13. Previous analysis pointed to the partial occupancy of the 2a site by Sn atoms. The charge density analysis reveals the dominant metallic character of the chemical bonding at the 2a atomic position. Simulation of vacancies at the 2a site using the virtual crystal approximation (VCA) indicate that the magnetic properties of Ce3Rh4Sn13 strongly depend on the Sn content, which could explain the discrepancy in magnetic properties between different Ce3Rh4Sn13 samples.

Structural transformation with "negative volume expansion": Chemical bonding and physical behavior of TiGePt

The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.

Experimental determination of the Fermi surface ofSr3Ir4Sn13

The stannide family of materials

Local magnetism in MnSiPt rules the chemical bond

{A}_{3}{T}_{4}{\mathrm{Sn}}_{13}

Coexistence of magnetic order and valence fluctuations in the Kondo lattice system Ce2Rh3Sn5

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Nonuniversality of the non-Fermi-liquid state inCeRhSb1−xSnxcompounds on the Sn-rich side

A\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}\mathrm{La},\mathrm{Sr},\mathrm{Ca}

Electronic structure and thermodynamic properties of CeRh(2)Sn(4) and LaRh(2)Sn(4).

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Electronic structure and thermodynamic properties of CeRh2Sn4 and LaRh2Sn4

T\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}\mathrm{Ir},\mathrm{Rh}

Electronic structure of CeRhX (X = Sn, In)

) is interesting due to the interplay between a tunable lattice instability and phonon-mediated superconductivity with