146 research outputs found
Enhanced moments of Eu in single crystals of the metallic helical antiferromagnet EuCo2 yAs2
The compound EuCo{2-y}As2 with the tetragonal ThCr2Si2 structure is known to
contain Eu{+2} ions with spin S = 7/2 that order below a temperature TN = 47 K
into an antiferromagnetic (AFM) proper helical structure with the ordered
moments aligned in the tetragonal ab plane, perpendicular to the helix axis
along the c axis, with no contribution from the Co atoms. Here we carry out a
detailed investigation of the properties of single crystals. Enhanced ordered
and effective moments of the Eu spins are found in most of our crystals.
Electronic structure calculations indicate that the enhanced moments arise from
polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical
resistivity measurements indicate metallic behavior. The low-field in-plane
magnetic susceptibilities chi{ab}(T < TN) for several crystals are reported
that are fitted well by unified molecular field theory (MFT), and the Eu-Eu
exchange interactions Jij are extracted from the fits. High-field magnetization
M data for magnetic fields H||ab reveal what appears to be a first-order
spin-flop transition followed at higher field by a second-order metamagnetic
transition of unknown origin, and then by another second-order transition to
the paramagnetic (PM) state. For H||c, the magnetization shows only a
second-order transition from the canted AFM to the PM state, as expected. The
critical fields for the AFM to PM transition are in approximate agreement with
the predictions of MFT. Heat capacity Cp measurements in zero and high H are
reported. Phase diagrams for H||c and H||ab versus T are constructed from the
high-field M(H,T) and Cp(H,T) measurements. The magnetic part Cmag(T, H = 0) of
Cp(T, H = 0) is extracted and is fitted rather well below TN by MFT, although
dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where
the molar entropy attains its high-T limit of R ln8.Comment: 29 pages, 30 figures including 62 subfigures, 8 tables, 84 reference
A brief review on mu SR studies of unconventional Fe and Cr based superconductors
Muon spin relaxation/rotation (muSR) is a vital technique for probing the
superconducting gap structure, pairing symmetry and time reversal symmetry
breaking, enabling an understanding of the mechanisms behind the unconventional
superconductivity of cuprates and Fe-based high-temperature superconductors,
which remain a puzzle. Very recently double layered Fe-based super-conductors
having quasi-2D crystal structures and Cr-based superconductors with a quasi-1D
structure have drawn considerable attention. Here we present a brief review of
the characteristics of a few selected Fe- and Cr-based superconducting
materials and highlight some of the major outstanding problems, with an
emphasis on the superconducting pairing symmetries of these materials. We focus
on muSR studies of the newly discovered superconductors ACa2Fe4As4F2(A = K, Rb,
and Cs), ThFeAsN, and A2Cr3As3(A = K, Cs), which were used to determine the
superconducting gap structures, the presence of spin fluctuations, and to
search for time reversal symmetry breaking in the superconducting states. We
also briefly discuss the results of muSR investigations of the
superconductivity in hole and electron doped BaFe2As2.Comment: Review paper, 23 pages, 11 figure
Magnetic behaviour of PrPd2B2C
We have synthesized a new quaternary borocarbide PrPdBC and
measured its magnetization, electrical resistivity and specific heat. The
compound crystallizes in the LuNiBC-type tetragonal structure
(space group {\it I4/mmm}). Above 100 K the magnetic susceptibility follows
Curie-Weiss behavior with effective moment = 3.60 , which
is very close to the value expected for Pr ions. We do not find evidence
for magnetic or superconducting transition down to 0.5 K. Specific heat
exhibits a broad Schottky type anomaly with a peak at 24 K, very likely related
to crystal electric field (CEF) excitation. The magnetic properties suggest the
presence of a singlet CEF ground state leading to a Van-Vleck paramagnetic
ground state.Comment: 2 pages, 2 figure
Understanding the magnetism in noncentrosymmetric CeIrGe3 Muon spin relaxation and neutron scattering studies
The magnetic properties of a pressure induced noncentrosymmetric
heavy-fermion superconductor CeIrGe have been investigated by muon spin
relaxation (SR), powder neutron diffraction (ND) and inelastic neutron
scattering (INS) techniques at ambient pressure. For completeness we have also
measured the ac magnetic susceptibility , dc magnetic
susceptibility , dc isothermal magnetization and heat capacity
down to 2 K. CeIrGe is known to exhibit pressure induced
superconductivity ( K) at a pressure of 20 GPa and
antiferromagnetic ordering at 8.7 K, 4.7 K and 0.7 K at ambient pressure. Our
and data show an additional anomaly near 6.2 K
which is also captured in data. From ,
and measurements we infer three antiferromagnetic
transitions above 2 K at K, K and K. Our SR study also confirms the presence of three transitions
through the observation of one frequency for ,
two frequencies for and three frequencies for
in the oscillatory asymmetry. The ND data reveal an
incommensurate nature of the magnetic ordering at K with the propagation
vector k = (0,0,0.688(3)), and a commensurate magnetic structure at K
with the propagation vector locked to the value k = (0,0,2/3) and magnetic
moments oriented along the axis. The commensurate structure couples a
macroscopic ferromagnetic component, resulting in a strong dependence of the
lock-in transition temperature on external magnetic field. The INS data show
two well defined crystal electric field (CEF) excitations arising from the
CEF-split Kramers doublet ground state of Ce.Comment: 13 pages, 16 figures, 1 tabl
Crystal electric field and possible coupling with phonons in Kondo lattice CeCuGa3
We investigate the magnetic and crystal electric field (CEF) states of the
Kondo lattice system CeCuGa3 by muon spin relaxation (muSR), neutron
diffraction, and inelastic neutron scattering (INS) measurements. A
noncentrosymmetric BaNiSn3-type tetragonal crystal structure (space group I4mm)
is inferred from x-ray as well as from neutron powder diffraction. The
low-temperature magnetic susceptibility and heat capacity data show an anomaly
near 2.3 - 2.5~K associated with long range magnetic ordering, which is further
confirmed by muSR and neutron diffraction data. The neutron powder diffraction
collected at 1.7 K shows the presence of magnetic Bragg peaks indexed by an
incommensurate magnetic propagation vector k = (0.148, 0.148, 0) and the
magnetic structure is best described by a longitudinal spin density wave with
ordered moments lying in ab-plane. An analysis of the INS data based on a CEF
model reveals the presence of two magnetic excitations near 4.5 meV and 6.9
meV. The magnetic heat capacity data suggest an overall CEF splitting of 20.7
meV, however the excitation between 20 and 30 meV is very broad and weak in our
INS data, but could provide an evidence of CEF level in this energy range in
agreement with the magnetic entropy. Our analysis of INS data based on the
CEF-phonon model indicates that the two excitations at 4.5 meV and 6.9 meV have
their origin in CEF-phonon coupling (i.e. splitting of one CEF peak into two
peaks, called vibron), with an overall splitting of 28.16 meV, similar to the
case of CeCuAl3 and CeAuAl3.Comment: 13 pages, 14 figure
Effect of 3 p and 5 d electron doping on the Kondo Semiconductor CeFe2Al10
We examined the effect of 3p and 5d electron doping on the Kondo semiconductor CeFe2Al10 by means of the electrical resistivity amp; 961; , magnetic susceptibility amp; 967; , and specific heat C measurements. The results show that in the 3p electron doped system CeFe2Al10 amp; 8722;ySiy, the semiconducting behavior is suppressed for y 0.05, and the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The Si substitution leads to a large decrease in the paramagnetic Weiss temperature amp; 952;P indicating a reduction in c f hybridization strength, however the Si does not induce magnetic order up to y 0.3 down to 2K. The systematic changes in amp; 961; T , amp; 967; T , and C T are similar to those for 5d electron doped system CeFe2 amp; 8722;xIrxAl10, although, Ir substitution induces a bulk antiferromagnetic transition below 3.1 K in CeFe1.7Ir0.3Al10. These changes can be explained by the collapse of the hybridization gap due to the suppression of the c f hybridization effect. Our results further confirm that the collapse of the spin charge gap by an excess electron doping is one of the universal features of the Kondo semiconductors CeT2Al10 T Fe, Ru, and O
Leprosy post-exposure prophylaxis with single-dose rifampicin
_Objective:_ Leprosy post-exposure prophylaxis with single-dose rifampicin (SDRPEP) has proven effective and feasible, and is recommended by WHO since 2018. This SDR-PEP toolkit was developed through the experience of the leprosy postexposure prophylaxis (LPEP) programme. It has been designed to facilitate and standardise the implementation of contact tracing and SDR-PEP administration in regions and countries that start the intervention.
_Results:_ Four tools were developed, incorporating the current evidence for SDRPEP and the methods and learnings from the LPEP project in eight countries.
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Search for gravitational-wave transients associated with magnetar bursts in advanced LIGO and advanced Virgo data from the third observing run
Gravitational waves are expected to be produced from neutron star oscillations associated with magnetar giant f lares and short bursts. We present the results of a search for short-duration (milliseconds to seconds) and longduration (∼100 s) transient gravitational waves from 13 magnetar short bursts observed during Advanced LIGO, Advanced Virgo, and KAGRA’s third observation run. These 13 bursts come from two magnetars, SGR1935 +2154 and SwiftJ1818.0−1607. We also include three other electromagnetic burst events detected by FermiGBM which were identified as likely coming from one or more magnetars, but they have no association with a known magnetar. No magnetar giant flares were detected during the analysis period. We find no evidence of gravitational waves associated with any of these 16 bursts. We place upper limits on the rms of the integrated incident gravitational-wave strain that reach 3.6 × 10−²³ Hz at 100 Hz for the short-duration search and 1.1 ×10−²² Hz at 450 Hz for the long-duration search. For a ringdown signal at 1590 Hz targeted by the short-duration search the limit is set to 2.3 × 10−²² Hz. Using the estimated distance to each magnetar, we derive upper limits upper limits on the emitted gravitational-wave energy of 1.5 × 1044 erg (1.0 × 1044 erg) for SGR 1935+2154 and 9.4 × 10^43 erg (1.3 × 1044 erg) for Swift J1818.0−1607, for the short-duration (long-duration) search. Assuming isotropic emission of electromagnetic radiation of the burst fluences, we constrain the ratio of gravitational-wave energy to electromagnetic energy for bursts from SGR 1935+2154 with the available fluence information. The lowest of these ratios is 4.5 × 103
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