155 research outputs found
Valence of cerium ions in selected ternary compounds from the system Ce-Rh-Sn
Over the last years, intermetallic compounds from the system Ce–Rh–Sn have attracted a considerable attention owing to a rich variety of strongly correlated electron phenomena they exhibit. CeRhSn2, Ce5Rh4Sn10, Ce2Rh3Sn5 and Ce3Rh4Sn13 are magnetically ordered heavy fermion systems [1-5]. Interestingly, for Ce3+xRh4Sn13-x (0.2<x<0.6) no sign of Kondo effect and long range magnetic order was found down to the temperature of 0.4 K [5]. In turn, CeRhSn shows non-Fermi liquid-type thermodynamic and transport properties at low temperatures [6-7] accompanied by an intermediate valence state of the Ce ions. Further, for CeRhSn, CeRhSn2 and CeRh2Sn4 spin fluctuations due to the Rh 4d electrons were also suggested [1,7-8]. The possible coexistence of magnetic phenomena originating from Ce and Rh makes the unequivocal interpretation of experimental data for these compounds very difficult. Consequently, a detailed understanding of the very complex physical properties/behavior requires the use of a broad spectrum of experimental methods, including extended thermodynamic and transport measurements as well as careful investigations of electronic structure. For these systems the full characterization of Ce 4f states in regard to their occupancy, localization in a conduction band and hybridization with the other valence band states is crucial for an unambiguous determination of ground state properties and the low energy excitations. Thus, X-ray absorption spectroscopy (XAS) is here of great use as a bulk probe which is highly sensitive on chemical states of elements. Furthermore, absorption measurements at the Ce LIII edge results in spectra with minimized lifetime broadening, largely unaffected by complicated many-electron final state effects. These spectra can be used to estimate the numbers for the fractional valence of Ce which originates from the strong hybridization between the Ce 4f and the other valence band states related to the valence fluctuation phenomena and/or to the formation of covalent bonds
Phonon-drag effect in FeGa3
The thermoelectric properties of single- and polycrystalline FeGa3 are
systematically investigated over a wide temperature range. At low temperatures,
below 20 K, previously not known pronounced peaks in the thermal conductivity
(400-800 W K^-1m-1) with corresponding maxima in the thermopower (in the order
of -16000 microV/K) were found in single crystalline samples. Measurements in
single crystals along [100] and [001] directions indicate only a slight
anisotropy in both the electrical and thermal transport. From susceptibility
and heat capacity measurements, a structural or magnetic phase transition was
excluded. Using density functional theory-based calculations, we have revisited
the electronic structure of FeGa3 and compared the magnetic (including
correlations) and non-magnetic electronic density of states. Thermopower at
fixed carrier concentrations are calculated using semi-classical Boltzmann
transport theory, and the calculated results match fairly with our experimental
data and exclude the possibility of strong electronic correlations as an
explanation for the low temperature enhancement. Eventually, after a careful
review, we assign the peaks in the thermopower as a manifestation of the
phonon-drag effect, which is supported by thermopower measurements in a
magnetic field.Comment: Phys. Rev. B accepted (2014
Superconducting gap structure of the skutterudite LaPt4Ge12 probed by specific heat and thermal transport
We investigated the superconducting order parameter of the filled
skutterudite LaPt4Ge12, with a transition temperature of Tc = 8.3 K. To this
end, we performed temperature and magnetic-field dependent specific-heat and
thermal-conductivity measurements. All data are compatible with a single
superconducting s-wave gap. However, a multiband scenario cannot be ruled out.
The results are discussed in the context of previous studies on the
substitution series Pr1-xLaxPt4Ge12. They suggest compatible order parameters
for the two end compounds LaPt4Ge12 and PrPt4Ge12. This is not consistent with
a single s-wave gap in LaPt4Ge12 considering previous reports of unconventional
and/or multiband superconductivity in PrPt4Ge12.Comment: 8 pages, 4 figure
Topological Hall effect in thin films of MnPtSn
Spin chirality in metallic materials with non-coplanar magnetic order can
give rise to a Berry phase induced topological Hall effect. Here, we report the
observation of a large topological Hall effect in high-quality films of
MnPtSn that were grown by means of magnetron sputtering on MgO(001).
The topological Hall resistivity is present up to T below
the spin reorientation transition temperature, ~K. We find, that the
maximum topological Hall resistivity is of comparable magnitude as the
anomalous Hall resistivity. Owing to the size, the topological Hall effect is
directly evident prior to the customarily performed subtraction of magnetometry
data. Further, we underline the robustness of the topological Hall effect in
Mn\textsubscript{2-x}PtSn by extracting the effect for multiple stoichiometries
(x~=~0.5, 0.25, 0.1) and film thicknesses (t = 104, 52, 35~nm) with maximum
topological Hall resistivities between cm and
cm at 150~K.Comment: 6 pages, 5 figure
Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation
The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated
by means of X-ray powder diffraction, electron diffraction, magnetic
susceptibility measurements and band structure calculations. Its structure is
similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin
system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements
reveal a spin gap-like behavior with \Delta ~ 270 K and a spin singlet ground
state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a
system of weakly coupled dimers in perfect agreement with the experimental
data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the
spin system in layered vanadium oxides by cation substitution. Simple
correlations between the cation size, geometrical parameters and exchange
integrals for the MV(2)O(5)-type oxides are established and discussed.Comment: 8 pages, 7 figure
Antiferromagnetic structure and electronic properties of BaCr2As2 and BaCrFeAs2
The chromium arsenides BaCr2As2 and BaCrFeAs2 with ThCr2Si2 type structure
(space group I4/mmm; also adopted by '122' iron arsenide superconductors) have
been suggested as mother compounds for possible new superconductors. DFT-based
calculations of the electronic structure evidence metallic antiferromagnetic
ground states for both compounds. By powder neutron diffraction we confirm for
BaCr2As2 a robust ordering in the antiferromagnetic G-type structure at T_N =
580 K with mu_Cr = 1.9 mu_B at T = 2K. Anomalies in the lattice parameters
point to magneto-structural coupling effects. In BaCrFeAs2 the Cr and Fe atoms
randomly occupy the transition-metal site and G-type order is found below 265 K
with mu_Cr/Fe = 1.1 mu_B. 57Fe Moessbauer spectroscopy demonstrates that only a
small ordered moment is associated with the Fe atoms, in agreement with
electronic structure calculations with mu_Fe ~ 0. The temperature dependence of
the hyperfine field does not follow that of the total moments. Both compounds
are metallic but show large enhancements of the linear specific heat
coefficient gamma with respect to the band structure values. The metallic state
and the electrical transport in BaCrFeAs2 is dominated by the atomic disorder
of Cr and Fe and partial magnetic disorder of Fe. Our results indicate that
Neel-type order is unfavorable for the Fe moments and thus it is destabilized
with increasing iron content.Comment: 14 pages, 14 figures, submitted to Physical Review
Thickness dependence of the anomalous Hall effect in thin films of the topological semimetal CoMnGa
Topological magnetic semimetals promise large Berry curvature through the
distribution of the topological Weyl nodes or nodal lines and further novel
physics with exotic transport phenomena. We present a systematic study of the
structural and magnetotransport properties of CoMnGa films from thin (20
nm) to bulk like behavior (80 nm), in order to understand the underlying
mechanisms and the role on the topology. The magnetron sputtered CoMnGa
films are -ordered showing very good heteroepitaxy and a
strain-induced tetragonal distortion. The anomalous Hall conductivity was found
to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall
angle of 13 %, which is comparatively larger than topologically trivial metals.
There is a good agreement between the theoretical calculations and the Hall
conductivity observed for the 80 nm film, which suggest that the effect is
intrinsic. Thus, the CoMnGa compound manifests as a promising material
towards topologically-driven spintronic applications.Comment: 7 pages, 5 figures, 1 tabl
Large anomalous Hall effect in the kagome ferromagnet LiMnSn
Kagome magnets are believed to have numerous exotic physical properties due
to the possible interplay between lattice geometry, electron correlation and
band topology. Here, we report the large anomalous Hall effect in the kagome
ferromagnet LiMnSn, which has a Curie temperature of 382 K and easy
plane along with the kagome lattice. At low temperatures, unsaturated positive
magnetoresistance and opposite signs of ordinary Hall coefficient for
and indicate the coexistence of electrons and holes in
the system. A large intrinsic anomalous Hall conductivity of 380
cm, or 0.44 per Mn layer, is observed in . This
value is significantly larger than those in other MnSn ( = rare
earth elements) kagome compounds. Band structure calculations show several band
crossings, including a spin-polarized Dirac point at the K point, close to the
Fermi energy. The calculated intrinsic Hall conductivity agrees well with the
experimental value, and shows a maximum peak near the Fermi energy. We
attribute the large anomalous Hall effect in LiMnSn to the band
crossings closely located near the Fermi energy
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