100 research outputs found
Electrical Resistivity and Thermal Expansion Measurements of URu2Si2 under Pressure
We carried out simultaneous measurements of electrical resistivity and
thermal expansion of the heavy-fermion compound URu2Si2 under pressure using a
single crystal. We observed a phase transition anomaly between hidden (HO) and
antiferromagnetic (AFM) ordered states at TM in the temperature dependence of
both measurements. For the electrical resistivity, the anomaly at TM was very
small compared with the distinct hump anomaly at the phase transition
temperature T0 between the paramagnetic state (PM) and HO, and exhibited only a
slight increase and decrease for the I // a-axis and c-axis, respectively. We
estimated each excitation gap of HO, Delta_HO, and AFM, Delta_AFM, from the
temperature dependence of electrical resistivity; Delta_HO and Delta_AFM have
different pressure dependences from each other. On the other hand, the
temperature dependence of thermal expansion exhibited a small anomaly at T0 and
a large anomaly at TM. The pressure dependence of the phase boundaries of T0
and TM indicates that there is no critical end point and the two phase
boundaries meet at the critical point.Comment: 4 pages, 4 figure
Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru_{1-x}Rh_x)_2Si_2 (x <= 0.05)
We have performed elastic and inelastic neutron scattering experiments on the
solid solutions U(Ru_{1-x}Rh_x)_2Si_2 for the Ru rich concentrations: x=0,
0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with
increasing x, and correspondingly the onset temperature T_m (~ 17.5 K at x=0)
of weak antiferromagnetic (AF) Bragg reflection decreases. For x=0.04 and 0.05,
no magnetic order is detected in the investigated temperature range down to 1.4
K. In the middle range, 0.02 <= x <= 0.03, we found that the AF Bragg
reflection is strongly enhanced. At x=0.02, this takes place at ~ 7.7 K (=T_M),
which is significantly lower than T_m (~ 13.7 K). T_M increases with increasing
x, and seems to merge with T_m at x=0.03. If the AF state is assumed to be
homogeneous, the staggered moment \mu_o estimated at 1.4 K increases from
0.02(2) \mu_B/U (x=0) to 0.24(1) \mu_B/U (x=0.02). The behavior is similar to
that observed under hydrostatic pressure (\mu_o increases to ~ 0.25 \mu_B/U at
1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an
increase in the AF volume fraction. We also found that the magnetic excitation
observed at Q=(1,0,0) below T_m disappears as T is lowered below T_M.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Point-contact spectroscopy on URuSi
Tunnel and point contact experiments have been made in a URuSi single
crystal along the c-axis. The experiments were performed changing temperature
and contact size in a low temperature scanning tunneling microscope. A
resonance develops at the Fermi level at K. This resonance splits
and becomes asymmetric when the 17.5 K phase transition is crossed. These
results are consistent with the existence of Kondo like bound states of the
U ionic configurations and the conduction electrons. Below the
transition, these configurations are split by the development of quadrupolar
ordering. The peak separation can be interpreted as a direct measurement of the
order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also
reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure
Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect
By using a highly sensitive homemade AC magnetic susceptibility technique,
the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals
with giant screw dislocations (having the structure of the Archimedean spirals)
exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height
c=1.2nm (the last parameter is responsible for creation of extended weak-link
structure around the giant defects). The magnetic field applied parallel to the
surface enters winding around the weak-link regions of the screw in the form of
the so-called spiral Josephson fluxons characterized by the temperature
dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon
structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw
dislocations) and manifests itself as a pronounced low-field peak in the
dependence of the susceptibility on magnetic field (applied normally to the
surface) in the form resembling the high-field (Abrikosov) fishtail effect.Comment: see also http://www.jetpletters.ac.ru/ps/1886/article_28701.shtm
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Inductively Heated Shape Memory Polymer for the Magnetic Actuation of Medical Devices
Presently there is interest in making medical devices such as expandable stents and intravascular microactuators from shape memory polymer (SMP). One of the key challenges in realizing SMP medical devices is the implementation of a safe and effective method of thermally actuating various device geometries in vivo. A novel scheme of actuation by Curie-thermoregulated inductive heating is presented. Prototype medical devices made from SMP loaded with Nickel Zinc ferrite ferromagnetic particles were actuated in air by applying an alternating magnetic field to induce heating. Dynamic mechanical thermal analysis was performed on both the particle-loaded and neat SMP materials to assess the impact of the ferrite particles on the mechanical properties of the samples. Calorimetry was used to quantify the rate of heat generation as a function of particle size and volumetric loading of ferrite particles in the SMP. These tests demonstrated the feasibility of SMP actuation by inductive heating. Rapid and uniform heating was achieved in complex device geometries and particle loading up to 10% volume content did not interfere with the shape recovery of the SMP
Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2
We have performed elastic neutron-scattering experiments on the
heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found
that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly
enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at
1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m
increases slightly at a rate ~ 1 K/GPa, roughly following the transition
temperature T_o determined from macroscopic anomalies. We have also observed a
sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of
antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced
lattice constant.Comment: RevTeX, 4 pages, 4 eps figures, accepted for publication in Phys.
Rev. Let
Current density inhomogeneity throughout the thickness of superconducting films and its effect on their irreversible magnetic properties
We calculate the distribution of the current density in superconducting
films along the direction of an external field applied perpendicular to the
film plane. Our analysis reveals that in the presence of bulk pinning is
inhomogeneous on a length scale of order the inter vortex distance. This
inhomogeneity is significantly enhanced in the presence of surface pinning. We
introduce new critical state model, which takes into account the current
density variations throughout the film thickness, and show how these variations
give rise to the experimentally observed thickness dependence of and
magnetic relaxation rate.Comment: RevTex, 9 PS figures. To appear in Phys. Rev.
Sex Pheromone of Lonomia obliqua: Daily Rhythm of Production, Identification, and Synthesis
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