99 research outputs found
Effect of Y substitution on the structural and magnetic properties of Dy1-xYxCo5 compounds
Structural and magnetization studies were carried out on Dy1-xYxCo5 [x = 0,
0.2, 0.4, 0.6, 0.8, 1] compounds which crystallize in the hexagonal CaCu5-type
structure. Lattice parameters and unit-cell volume increase with Y
concentration. Large thermomagnetic irreversibility between the field-cooled
and the zero-field cooled magnetization data has been observed in all the
compounds, which has been attributed to the domain wall pinning effect.
Temperature dependence of magnetization data shows that except DyCo5 and YCo5,
all the compounds show spin reorientation transitions in the range of 5-300 K.
The spin reorientation temperature decreases from 266 K for x=0.2 to 100 K for
x=0.8. Powder x-ray diffractograms of the magnetically aligned samples show
that DyCo5 has planar anisotropy at room temperature whereas all the other
compounds possess axial anisotropy. The spin reorientation transition has been
attributed to a change in the easy magnetization direction from the ab-plane to
the c-axis, as the temperature is increased. The anisotropy field and the first
order anisotropy constant are found to be quite high in all the compounds
except DyCo5. The magnetic properties have been explained by taking into
account the variations in contributions arising from the rare earth and
transition metal sublattices.Comment: 12 pages, 7 figure
Magnetic, magnetocaloric and magnetotransport properties of RSn_{1+x}Ge_{1-x} compounds (R=Gd, Tb, Er; x=0.1)
We have studied the magnetic, magnetocaloric and magnetotransport properties
of RSn1+xGe1-x(R=Gd, Tb, Er; x=0.1) series by means of magnetization, heat
capacity and resistivity measurements. It has been found that all the compounds
crystallize in the orthorhombic crystal structure described by the
centrosymmetric space group Cmcm (No. 63). The magnetic susceptibility and heat
capacity data suggest that all the compounds are antiferromagnetic. Large
negative values of {\theta}p in case of GdSn1.1Ge0.9 and TbSn1.1Ge0.9 indicate
that strong antiferromagnetic interactions are involved, which is also
reflected in the magnetization isotherms. On the other hand ErSn1.1Ge0.9 shows
weak antiferromagnetic interaction. The heat capacity data have been analyzed
by fitting the temperature dependence and the values of {\theta}D and {\gamma}
have been estimated. Among these three compounds, ErSn1.1Ge0.9 shows
considerable magnetic entropy change of 9.5 J/kg K and an adiabatic temperature
change of 3.2 K for a field of 50 kOe. The resistivity data in different
temperature regimes have been analyzed and the dominant contributions have been
identified. All the compounds show small but positive magnetoresistance.Comment: 23 pages,11 figure
Magnetocaloric effect in the intermetallic compound DyNi
Magnetic and heat capacity measurements have been carried out on the
polycrystalline sample of DyNi which crystallizes in the orthorhombic FeB
structure (space group Pnma). This compound is ferromagnetic with a Curie
temperature of 59 K. Magnetization-field isotherms at low temperatures shows a
step-like behavior characteristic of metamagnetic transitions. The
magnetocaloric effect has been measured both in terms of isothermal magnetic
entropy change and adiabatic temperature change for various applied magnetic
fields. The maximum values of the entropy change and the temperature change are
found to be 19 Jkg-1K-1 and 4.5 K, respectively, for a field of 60 kOe. The
large magnetocaloric effect is attributed to the field-induced spin-flop
metamagnetism occurring in this compound, which has a noncollinear magnetic
structure at low fields.Comment: 11 page
Metastable magnetization behavior in magnetocaloric R6Co1.67Si3 (R=Tb and Nd) compounds
Magnetic field and time induced steps have been observed in the recently
discovered ternary silicide R6Co1.67Si3. Huge relaxation steps are observed
across different loops in the low temperature magnetization isotherms. Giant
relaxation present in this system indicates the existence of incubation time to
get the saturated moment at a certain field. Measurement protocol sensitive
magnetization behavior observed in this system may arise from the strong
magnetostructural coupling and/or magnetic frustration. Electrical resistivity
and magnetoresistance also reflect the magnetic state of the compound.
Magnetocaloric effect is found to be large at temperatures close to the
magnetic transition temperature.Comment: 15 pages, 9 figure
Correlation between magnetism and magnetocaloric effect in RCo2-based Laves phase compounds
By virtue of the itinerant electron metamagnetism (IEM), the RCo2 compounds
with R=Er, Ho and Dy are found to show first order magnetic transition at their
ordering temperatures. The inherent instability of Co sublattice magnetism is
responsible for the occurrence of IEM, which leads to interesting magnetic and
related properties. The systematic studies of the variations in the magnetic
and magnetocaloric properties of the RCo2-based compounds show that the
magnetovolume effect plays a decisive role in determining the nature of
magnetic transitions and hence the magnetocaloric effect (MCE) in these
compound. It is found that the spin fluctuations arising due to the
magnetovolume effect reduce the strength of IEM in these compounds, which
subsequently lead to a reduction in the MCE. Most of the substitutions at the
Co site are found to result in a positive magnetovolume effect, leading to an
initial increase in the ordering temperature. Application of pressure, on the
other hand, causes a reduction in the ordering temperature due to the negative
magnetovolume effect. A comparative study of the magnetic and magnetocaloric
properties of RCo2 compounds under various substitutions and applied pressure
is presented. Analysis of the magnetization data using the Landau theory has
shown that there is a strong correlation between the Landau coefficient (B) and
the MCE. The variations seen in the order of magnetic transition and the MCE
values seem to support the recent model proposed by Khmelevskyi and Mohn for
the occurrence of IEM in RCo2 compounds
Erratum: "A Gravitational-wave Measurement of the Hubble Constant Following the Second Observing Run of Advanced LIGO and Virgo" (2021, ApJ, 909, 218)
[no abstract available
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b
We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society
Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run
Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society
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