133 research outputs found
Unconventional magnetism in multivalent charge-ordered YbPtGe probed by Pt- and Yb-NMR
Detailed Pt- and Yb nuclear magnetic resonance (NMR) studies
on the heterogeneous mixed valence system YbPtGe are reported. The
temperature dependence of the Pt-NMR shift indicates the
opening of an unusual magnetic gap below 200\,K. was analyzed by a
thermal activation model which yields an isotropic gap \,K. In contrast, the spin-lattice relaxation rate () does
not provide evidence for the gap. Therefore, an intermediate-valence picture is
proposed while a Kondo-insulator scenario can be excluded. Moreover,
() follows a simple metallic behavior, similar to the reference
compound YPtGe. A well resolved NMR line with small shift is assigned to
divalent Yb. This finding supports the proposed model with two sub-sets
of Yb species (di- and trivalent) located on the Yb2 and Yb1 site of the
YbPtGe lattice.Comment: Submitted in Physical Review B (Rapid Communication
Magnetic impurity resonance states and symmetry of the superconducting order parameter in iron-based superconductors
We investigate the effect of magnetic impurities on the local quasiparticle
density of states (LDOS) in iron-based superconductors. Employing the
two-orbital model where 3 electron and hole conduction bands are hybridizing
with the localized -orbital of the impurity spin, we investigate how various
symmetries of the superconducting gap and its nodal structure influence the
quasiparticle excitations and impurity bound states. We show that the bound
states behave qualitatively different for each symmetry. Most importantly we
find that the impurity-induced bound states can be used to identify the nodal
structure of the extended s-wave symmetry () that is actively
discussed in ferropnictides.Comment: 7 pages, 5 figures, theory part is extended, figures are replace
Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure
New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.Comment: RevTeX, 4 figures, submitted to Physical Review Letters July 12, 200
Evidence for time-reversal symmetry breaking in superconducting PrPt4Ge12
Zero and longitudinal field muon spin rotation (muSR) experiments were
performed on the superconductors PrPt4Ge12 and LaPt4Ge12. In PrPt4Ge12 below Tc
a spontaneous magnetization with a temperature variation resembling that of the
superfluid density appears. This observation implies time-reversal symmetry
(TRS) breaking in PrPt4Ge12 below Tc = 7.9 K. This remarkably high Tc for an
anomalous superconductor and the weak and gradual change of Tc and of the
related specific heat anomaly upon La substitution in La_(1-x)Pr_xPt_4Ge_(12)
suggests that the TRS breaking is due to orbital degrees of freedom of the
Cooper pairs.Comment: To appear in Phys. Rev. B. 5 pages, 3 figure
Charge-Doping driven Evolution of Magnetism and non-Fermi-Liquid Behavior in the Filled Skutterudite CePt4Ge12-xSbx
The filled-skutterudite compound CePt4Ge12 is situated close to the border
between intermediate-valence of Ce and heavy-fermion behavior. Substitution of
Ge by Sb drives the system into a strongly correlated and ultimately upon
further increasing the Sb concentration into an antiferromagnetically ordered
state. Our experiments evidence a delicate interplay of emerging Kondo physics
and the formation of a local 4f moment. An extended non-Fermi-liquid region,
which can be understood in the framework of a Kondo-disorder model, is
observed. Band-structure calculations support the conclusion that the physical
properties are governed by the interplay of electron supply via Sb substitution
and the concomitant volume effects.Comment: 5 pages, 3 Figur
Superconductivity induced by ruthenium substitution in an iron arsenide: investigation of SrFe2-xRuxAs2 (0 <= x <= 2)
The magnetism in SrFe2As2 can be suppressed by electron doping through a
small substitution of Fe by Co or Ni, giving way to superconductivity. We
demonstrate that a massive substitution of Fe by isovalent ruthenium similarly
suppresses the magnetic ordering in SrFe2-xRuxAs2 and leads to bulk
superconductivity for 0.6 <= x <= 0.8. Magnetization, electrical resistivity,
and specific heat data show Tc up to approx 20K. Detailed structural
investigations reveal a strong decrease of the lattice parameter ratio c/a with
increasing x. DFT band structure calculations are in line with the observation
that the magnetic order in SrFe2-xRuxAs2 is only destabilized for large x.Comment: 6 pages, 5 figures, extended and revised versio
Model of evaluation of the complex use and protection of water resources in hydrocontacting systems using the theory of urban logic (as example r. Zbruch, Ternopil region, Ukraine)
Ferromagnetism and superconductivity in P-doped CeFeAsO
We report on superconductivity in CeFeAs1-xPxO and the possible coexistence
with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with
ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering
temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K
and does not shift to lower temperatures with further increase of the P
concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K
which is widely discussed for the iron based superconductors can be excluded
for this alloy series. Surprisingly, thermal expansion and X-ray powder
diffraction indicate the absence of an orthorhombic distortion despite clear
evidence for short range AFM Fe-ordering from muon-spin-rotation measurements.
Furthermore, we discovered the formation of a sharp electron spin resonance
signal unambiguously connected with the emergence of FM ordering.Comment: 5 pages, 4 figures, published in Phys. Rev. B (Rapid Communication,
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Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1-xCrx(SO4)*6H2O crystals by metal ion substitution
Hybrid organometallic systems offer a wide range of functionalities,
including magnetoelectric interactions. However, the ability to design
on-demand ME coupling remains challenging despite a variety of host-guest
configurations and ME phases coexistence possibilities. Here, we report the
effect of metal-ion substitution on the magnetic and electric properties in the
paramagnetic ferroelectric DMAAS crystals. Doing so we are able to induce and
even tune a sign of the ME interactions in the paramagnetic ferroelectric
state. Both studied samples with 6.5% and 20% of Cr become paramagnetic,
contrary to the initial diamagnetic compound. Due to the isomorphous
substitution with Cr the ferroelectric phase transition temperature increases
nonlinearly, with the shift being larger for the sample with Cr content of
6.5%. A magnetic field applied along the polar c axis increases
ferroelectricity for this sample and shifts Tc to higher values, while inverse
effects are observed for sample containing 20% of Cr. The ME coupling
coefficient of 1.7ns/m found for a crystal with 20% of Cr is among the highest
reported up to now. The observed sign change of ME coupling coefficient with a
small change in Cr content paves the way for ME coupling engineering.Comment: 7 pages, 6 figures. New Organometallic Magnetoelectric and
Ferroelectric compoun
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