415 research outputs found
Heat Capacity of the Pressure-induced Superconductivity in Itinerant Ferromagnet UGe
Recently co-existence of the ferromagnetism and superconductivity was
reported in the high-pressure region (1.0-1.6 GPa) in UGe. We performed the
heat capacity measurement on UGe under high pressure. At 1.13 GPa, we found
a peak corresponding to the superconducting transition. The superconducting
temperature and are 0.6 K and 0.25,
respectively. The superconducting transition was also confirmed by the
appearance of the Meissner effect in the {\it ac} susceptibility. From these
results, we confirm a bulk nature of the superconductivity in UGe. The
value of ( 95 mJ/moleK) just above at 1.15 GPa is as
much as 3 times larger than that at ambient pressure, which indicates a large
mass enhancement of quasiparticles under high pressure.Comment: submitted to the International Conference on Strongly Correlated
Electron Systems 200
Pressure-induced Superconductivity in a Ferromagnet UGe -- Resistivity Measurements in Magnetic Field --
The electrical resistivity measurements in the magnetic field are carried out
on the pressure-induced superconductor UGe. The superconductivity is
observed from 1.06 to 1.44 GPa. The upper critical field of is
anisotropic where exhibits positive curvature for and
-axis. The characteristic enhancement of is reconfirmed for
-axis. In the temperature and field dependence of resistivity at where the ferromagnetic ordering disappears, it is observed that the
application of the external field along the {\it a}-axis increases the
coefficient of Fermi liquid behavior correspondingly to the
metamagnetic transition.Comment: To be published in the proceeding of the International Conference on
High Pressure Science and Technology(AIRAPT-18),Beijing,China,23-27 July 200
Relationships between seismicity and slow slip events at New Zealand's northern and central Hikurangi subduction zone inferred from detailed spatiotemporal earthquake analysis
Tohoku University博士(理学)thesi
Pressure-induced ferromagnetism with strong Ising-type anisotropy in YbCuSi
We report dc magnetic measurements on YbCuSi at pressures above 10
GPa using a miniature ceramic anvil cell. YbCuSi shows a
pressure-induced transition from the non-magnetic to a magnetic phase at 8 GPa.
We find a spontaneous dc magnetization in the pressure-induced phase above 9.4
GPa. The pressure dependence of the ferromagnetic transition temperature T_C
and the spontaneous magnetic moment m_0 at 2.0 K have been determined. The
value of m_0 in the present macroscopic measurement is less than half of that
determined via Mossbauer experiment. The difference may be attributed to
spatial phase separation between the ferromagnetic and paramagnetic phases.
This separation suggests that the pressure-induced phase boundary between the
paramagnetic and ferromagnetic states is of first order. Further, we have
studied the magnetic anisotropy in the pressure-induced ferromagnetic state.
The effect of pressure on the magnetization with magnetic field along the
magnetic easy -axis is much larger than for field along the hard -axis in
the tetragonal structure. The pressure-induced phase has strong Ising-type
uniaxial anisotropy, consistent with the two crystal electric field (CEF)
models proposed for YbCuSi.Comment: 5 pages, 3 figure
Dynamical properties of S=1 bond-alternating Heisenberg chains in transverse magnetic fields
We calculate dynamical structure factors of the S=1 bond-alternating
Heisenberg chain with a single-ion anisotropy in transverse magnetic fields,
using a continued fraction method based on the Lanczos algorithm. In the
Haldane-gap phase and the dimer phase, dynamical structure factors show
characteristic field dependence. Possible interpretations are discussed. The
numerical results are in qualitative agreement with recent results for
inelastic neutron-scattering experiments on the S=1 bond-alternating
Heisenberg-chain compound and the
S=1 Haldane-gap compound in
transverse magnetic fields.Comment: 7 pages, 6 figure
Pressure-temperature Phase Diagram of Polycrystalline UCoGe Studied by Resistivity Measurement
Recently, coexistence of ferromagnetism (T_Curie = 2.8K) and
superconductivity (T_sc = 0.8K) has been reported in UCoGe, a compound close to
a ferromagnetic instability at ambient pressure P. Here we present resistivity
measurements under pressure on a UCoGe polycrystal. The phase diagram obtained
from resistivity measurements on a polycrystalline sample is found to be
qualitatively different to those of all other ferromagnetic superconductors. By
applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No
indication of ferromagnetic order has been observed above P ~ 1GPa. The
resistive superconducting transition is, however, quite stable in temperature
and persists up to the highest measured pressure of about 2.4GPa.
Superconductivity would therefore appear also in the paramagnetic phase.
However, the appearance of superconductivity seems to change at a
characteristic pressure P* ~ 0.8GPa. Close to a ferromagnetic instability, the
homogeneity of the sample can influence strongly the electronic and magnetic
properties and therefore bulk phase transitions may differ from the
determination by resistivity measurements.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Unconventional critical scaling of magnetization in uranium ferromagnetic superconductors UGe and URhGe
We report a dc magnetization study of the critical phenomenon around the
ferromagnetic transition temperature T_C in high-quality single crystals of
uranium ferromagnetic superconductors UGe2 and URhGe. The critical exponents,
beta for the temperature dependence of the magnetization below T_C, gamma for
the magnetic susceptibility, and delta for the magnetic isothermal at T_C have
been determined with a modified Arrott plot, a Kouvel-Fisher plot, and the
scaling analysis. Magnetization in the ferromagnetic state has strong uniaxial
magnetic anisotropy in the two compounds. However, the universality class of
the critical phenomena do not belong to the three dimensional (3D) Ising
system. Although the values of beta in UGe2 and URhGe are close to those in the
3D magnets, the values of gamma are close to unity, that expected from the mean
field theory. Similar critical exponents have been reported previously for the
3D Ising ferromagnet UIr where superconductivity appears under high pressure.
The critical behavior may be limited to a very narrow Ginzburg critical region
of 1 mK because of the strong itinerant character of the 5f electrons in the
ferromagnetic superconductor UCoGe where the mean field behavior of the
magnetization has been reported. The unconventional critical scaling of
magnetization in UGe2, URhGe and UIr cannot be explained via previous
approaches to critical phenomena. The ferromagnetic correlation between the 5f
electrons differs from that in the 3D Ising system and this difference may be a
key point for the understanding of the ferromagnetism where superconductivity
emerges.Comment: 8 pages, 5 figure
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