764 research outputs found
Magnetization study on the field-induced quantum critical point in YbRh_2Si_2
We study the field-induced quantum critical point (QCP) in YbRhSi by
low-temperature magnetization, , and magnetic Gr\"uneisen ratio,
, measurements and compare the results with previous thermal
expansion, , and critical Gr\"uneisen ratio, , data
on YbRh(SiGe). In the latter case, a slightly
negative chemical pressure has been used to tune the system towards its
zero-field QCP. The magnetization derivative is far more singular than
thermal expansion, reflecting a strongly temperature dependent pressure
derivative of the field at constant entropy,
(: molar volume), which saturates at T/GPa for .
The line , previously observed in Hall- and thermodynamic
measurements, separates regimes in - phase space of stronger
) and weaker ) divergent .Comment: 4 Pages, 3 Figures, submitted to Proceedings of ICM 2009 (Karlsruhe
Ferromagnetic quantum critical fluctuations in YbRh_2(Si_{0.95}Ge_{0.05})_2
The bulk magnetic susceptibility of
YbRh(SiGe) has been investigated %by ac-and
dc-magnetometry at low temperatures and close to the field-induced quantum
critical point at T. For T a Curie-Weiss law with a
negative Weiss temperature is observed at temperatures below 0.3 K. Outside
this region, the susceptibility indicates ferromagnetic quantum critical
fluctuations: above 0.3 K, while at low temperatures
the Pauli susceptibility follows and scales with
the coefficient of the term in the electrical resistivity. The
Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the
critical field.Comment: Physical Review Letters, to be publishe
Divergence of the Magnetic Gr\"{u}neisen Ratio at the Field-Induced Quantum Critical Point in YbRhSi
The heavy fermion compound YbRhSi is studied by low-temperature
magnetization and specific-heat measurements at magnetic fields
close to the quantum critical point ( T, ). Upon
approaching the instability, is more singular than , leading to a
divergence of the magnetic Gr\"uneisen ratio .
Within the Fermi liquid regime, with
and T which is consistent with
scaling behavior of the specific-heat coefficient in
YbRh(SiGe). The field-dependence of indicates
an inflection point of the entropy as a function of magnetic field upon passing
the line previously observed in Hall- and thermodynamic
measurements.Comment: 4 pages, 3 Figure
Effect of Ni-doping on magnetism and superconductivity in Eu0.5K0.5Fe2As2
The effect of Ni-doping on the magnetism and superconductivity in
Eu0.5K0.5Fe2As2 has been studied through a systematic investigation of magnetic
and superconducting properties of Eu0.5K0.5(Fe1-xNix)2As2 (x = 0, 0.03, 0.05,
0.08 and 0.12) compounds by means of dc and ac magnetic susceptibilities,
electrical resistivity and specific heat measurements. Eu0.5K0.5Fe2As2 is known
to exhibit superconductivity with superconducting transition temperature Tc as
high as 33 K. The Ni-doping leads to a rapid decrease in Tc; Tc is reduced to
23 K with 3% Ni-doping, and 8% Ni-doping suppresses the superconductivity to
below 1.8 K. In 3% Ni-doped sample Eu0.5K0.5(Fe0.97Ni0.03)2As2
superconductivity coexists with short range ordering of Eu2+ magnetic moments
at Tm ~ 6 K. The suppression of superconductivity with Ni-doping is accompanied
with the emergence of a long range antiferromagnetic ordering with TN = 8.5 K
and 7 K for Eu0.5K0.5(Fe0.92Ni0.08)2As2 and Eu0.5K0.5(Fe0.88Ni0.12)2As2,
respectively. The temperature and field dependent magnetic measurements for x =
0.08 and 0.12 samples reflect the possibility of a helical magnetic ordering of
Eu2 moments. We suspect that the helimagnetism of Eu spins could be responsible
for the destruction of superconductivity as has been observed in Co-doped
EuFe2As2. The most striking feature seen in the resistivity data for x = 0.08
is the reappearance of the anomaly presumably due to spin density wave
transition at around 60 K. This could be attributed to the compensation of
holes (K-doping at Eu-site) by the electrons (Ni-doping at Fe site). The
anomaly associated with spin density wave further shifts to 200 K for x = 0.12
for which the electron doping has almost compensated the holes in the system.Comment: 9 pages, 10 figure
From Thy Lowest Depths, O Sea
https://digitalcommons.library.umaine.edu/mmb-vp/3108/thumbnail.jp
Self-supervised automated wrapper generation for weblog data extraction
Data extraction from the web is notoriously hard. Of the types of resources available on the web, weblogs are becoming increasingly important due to the continued growth of the blogosphere, but remain poorly explored. Past approaches to data extraction from weblogs have often involved manual intervention and suffer from low scalability. This paper proposes a fully automated information extraction methodology based on the use of web feeds and processing of HTML. The approach includes a model for generating a wrapper that exploits web feeds for deriving a set of extraction rules automatically. Instead of performing a pairwise comparison between posts, the model matches the values of the web feeds against their corresponding HTML elements retrieved from multiple weblog posts. It adopts a probabilistic approach for deriving a set of rules and automating the process of wrapper generation. An evaluation of the model is conducted on a dataset of 2,393 posts and the results (92% accuracy) show that the proposed technique enables robust extraction of weblog properties and can be applied across the blogosphere for applications such as improved information retrieval and more robust web preservation initiatives
Field-induced suppression of the heavy-fermion state in YbRh_2Si_2
We report DC magnetization measurements on YbRh_2Si_2 at temperatures down to
0.04K, magnetic fields B<11.5T and under hydrostatic pressure P<1.3GPa. At
ambient pressure a kink at B*=9.9T indicates a new type of field-induced
transition from an itinerant to a localized 4f-state. This transition is
different from the metamagnetic transition observed in other heavy fermion
compounds, as here ferromagnetic rather than antiferromagnetic correlations
dominate below B*. Hydrostatic pressure experiments reveal a clear
correspondence of B* to the characteristic spin fluctuation temperature
determined from specific heat
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