25 research outputs found
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
Local magnetism in MnSiPt rules the chemical bond
A crystal structure can be understood as a result of bonding interactions (covalent, ionic, van der Waals, etc.) between the constituting atoms. If the forces caused by these interactions are equilibrated, the so-stabilized crystal structure should have the lowest energy. In such an atomic configuration, additional weaker atomic interactions may further reduce the total energy, influencing the final atomic arrangement. Indeed, in the intermetallic compound MnSiPt, a 3D framework is formed by polar covalent bonds between Mn, Si, and Pt atoms. Without taking into account the local spin polarization of manganese atoms, they would form MnāMn bonds within the framework. Surprisingly, the local magnetic moments of manganese prevent the formation of MnāMn bonds, thus changing decisively and significantly the final atomic arrangement.Among intermetallic compounds, ternary phases with the simple stoichiometric ratio 1:1:1 form one of the largest families. More than 15 structural patterns have been observed for several hundred compounds constituting this group. This, on first glance unexpected, finding is a consequence of the complex mechanism of chemical bonding in intermetallic structures, allowing for large diversity. Their formation process can be understood based on a hierarchy of energy scales: The main share is contributed by covalent and ionic interactions in accordance with the electronic needs of the participating elements. However, smaller additional atomic interactions may still tip the scales. Here, we demonstrate that the local spin polarization of paramagnetic manganese in the new compound MnSiPt rules the adopted TiNiSi-type crystal structure. Combining a thorough experimental characterization with a theoretical analysis of the energy landscape and the chemical bonding of MnSiPt, we show that the paramagnetism of the Mn atoms suppresses the formation of MnāMn bonds, deciding between competing crystal structures
muSR and Magnetometry Study of the Type-I Superconductor BeAu
We present muon spin rotation and relaxation (muSR) measurements as well as
demagnetising field corrected magnetisation measurements on polycrystalline
samples of the noncentrosymmetric superconductor BeAu. From muSR measurements
in a transverse field, we determine that BeAu is a type-I superconductor with
Hc = 256 Oe, amending the previous understanding of the compound as a type-II
superconductor. To account for demagnetising effects in magnetisation
measurements, we produce an ellipsoidal sample, for which a demagnetisation
factor can be calculated. After correcting for demagnetising effects, our
magnetisation results are in agreement with our muSR measurements. Using both
types of measurements we construct a phase diagram from T = 30 mK to Tc = 3.25
K. We then study the effect of hydrostatic pressure and find that 450 MPa
decreases Tc by 34 mK, comparable to the change seen in type-I elemental
superconductors Sn, In and Ta, suggesting BeAu is far from a quantum critical
point accessible by the application of pressure.Comment: 10 pages, 8 figure
Complex magnetic phase diagram of metamagnetic MnPtSi.
The magnetic, thermal and transport properties as well as electronic band structure of MnPtSi are reported. MnPtSi is a metal that undergoes a ferromagnetic transition at T_C = 340(1) K and a spināreorientation transition at T_N = 326(1) K to an antiferromagnetic phase. Firstāprinciples electronic structure calculations indicate a notāfully polarized spin state of Mn in a d^5 electron conļ¬guration with J = S = 3/2, in agreement with the saturation magnetization of 3 Āµ_B per f.u. in the ordered state and the observed paramagnetic eļ¬ective moment. A sizeable anomalous Hall eļ¬ect in the antiferromagnetic phase alongside the computational study suggests that the antiferromagnetic structure is noncollinear. Based on thermodynamic measurements and resistivity data we construct a magnetic phase diagram. Magnetization curves M(H) at low temperatures reveal a metamagnetic transition of spināļ¬op type. The spin-ļ¬opped phase terminates at a critical point with T_cr ā 300 K
and H_cr ā 10 kOe, near which a peak of the magnetocaloric entropy change is observed. Using Arrott plot analysis and magnetoresistivity data we argue that the metamagnetic transition is of a ļ¬rstāorder type, whereas the strong ļ¬eld dependence of T_N and the linear relationship of the T_N with M^2 hint at its magnetoelastic nature
Complex magnetic phase diagram of metamagnetic MnPtSi
The magnetic, thermal and transport properties as well as electronic band structure of MnPtSi are reported. MnPtSi is a metal that undergoes a ferromagnetic transition at T_C = 340(1) K and a spināreorientation transition at T_N = 326(1) K to an antiferromagnetic phase. Firstāprinciples electronic structure calculations indicate a notāfully polarized spin state of Mn in a d^5 electron conļ¬guration with J = S = 3/2, in agreement with the saturation magnetization of 3 Āµ_B per f.u. in the ordered state and the observed paramagnetic eļ¬ective moment. A sizeable anomalous Hall eļ¬ect in the antiferromagnetic phase alongside the computational study suggests that the antiferromagnetic structure is nonācollinear. Based on thermodynamic measurements and resistivity data we construct a magnetic phase diagram. Magnetization curves M(H) at low temperatures reveal a metamagnetic transition of spināļ¬op type. The spin-ļ¬opped phase terminates at a critical point with T_cr ā 300 K
and H_cr ā 10 kOe, near which a peak of the magnetocaloric entropy change is observed. Using Arrott plot analysis and magnetoresistivity data we argue that the metamagnetic transition is of a ļ¬rstāorder type, whereas the strong ļ¬eld dependence of T_N and the linear relationship of the T_N with M^2 hint at its magnetoelastic nature
Anisotropic superconductivity and quantum oscillations in the layered dichalcogenide TaSnS2
TaSnS2 single crystal and polycrystalline samples are investigated in detail by magnetization, electrical resistivity, and specific heat as well as Raman spectroscopy and nuclear magnetic resonance (NMR). Studies are focused on the temperature and magnetic field dependence of the superconducting state. We determine the critical fields for both directions Bā„c and Bā„c. Additionally, we investigate the dependence of the resistivity, the critical temperature, and the structure through Raman spectroscopy under high pressure up to 10 GPa. At a pressure of ā3GPa the superconductivity is suppressed below our minimum temperature. The Sn NMR powder spectrum shows a single line which is expected for the TaSnS2 phase and confirms the high sample quality. Pronounced de Haas-van Alphen oscillations in the ac susceptibility of polycrystalline sample reveal two pairs of frequencies indicating coexisting small and large Fermi surfaces. The effective mass of the smaller Fermi surface is ā0.5me. We compare these results with the band structures from DFT calculations. Our findings on TaSnS2 are discussed in terms of a quasi-two-dimensional BCS superconductivity
AFe2As2 (A = Ca, Sr, Ba, Eu) and SrFe_(2-x)TM_(x)As2 (TM = Mn, Co, Ni): crystal structure, charge doping, magnetism and superconductivity
The electronic structure and physical properties of the pnictide compound
families OFeAs ( = La, Ce, Pr, Nd, Sm), FeAs ( = Ca,
Sr, Ba, Eu), LiFeAs and FeSe are quite similar. Here, we focus on the members
of the FeAs family whose sample composition, quality and single
crystal growth are better controllable compared to the other systems. Using
first principles band structure calculations we focus on understanding the
relationship between the crystal structure, charge doping and magnetism in
FeAs systems. We will elaborate on the tetragonal to
orthorhombic structural distortion along with the associated magnetic order and
anisotropy, influence of doping on the site as well as on the Fe site, and
the changes in the electronic structure as a function of pressure.
Experimentally, we investigate the substitution of Fe in
SrFeAs by other 3 transition metals, = Mn, Co, Ni.
In contrast to a partial substitution of Fe by Co or Ni (electron doping) a
corresponding Mn partial substitution does not lead to the supression of the
antiferromagnetic order or the appearance of superconductivity. Most calculated
properties agree well with the measured properties, but several of them are
sensitive to the As position. For a microscopic understanding of the
electronic structure of this new family of superconductors this structural
feature related to the Fe-As interplay is crucial, but its correct ab initio
treatment still remains an open question.Comment: 27 pages, single colum
Chemical and Physical Properties of MnPtSi
The new intermetallic compound MnPtSi was synthesized, and its crystal structure was solved and refined from single-crystal X-ray diffraction data. MnPtSi crystallizes in the orthorhombic TiNiSi structure type.1 The microstructure of polycrystalline samples show strong twinning. Structural phase transitions within the AlB2 structure family were observed in similar systems (MnNiGe, MnCoGe2). Therefore, we investigated the homogeneity range and performed in-situ high-temperature diffraction measurements. No high-temperature modification was observed. Theoretical calculations to confirm the experimental founding and give an explanation for the stability of the orthorhombic structure are in process