35 research outputs found
Yb-based heavy fermion compounds and field tuned quantum criticality
The thermoelectric properties of the heavy fermions YbT2Zn20(T = Fe, Ru, Os, Ir, Rh, and Co) and YbAgGe have been investigated as a function of magnetic field and temperature. Measurements of the thermodynamic and transport properties of YbPtBi suggest that a quantum critical point may be induced by an applied magnetic field
Experimental Setup for the Measurement of the Thermoelectric Power in Zero and Applied Magnetic Field
An experimental setup was developed for the measurement of the thermoelectric
power (TEP, Seebeck coefficient) in the temperature range from 2 to 350 K and
magnetic fields up to 140 kOe. The system was built to fit in a commercial
cryostat and is versatile, accurate and automated; using two heaters and two
thermometers increases the accuracy of the TEP measurement. High density data
of temperature sweeps from 2 to 350 K can be acquired in under 16 hours and
high density data of isothermal field sweeps from 0 to 140 kOe can be obtained
in under 2 hours. Calibrations for the system have been performed on a platinum
wire and BiSrCaCuO high superconductors.
The measured TEP of phosphor-bronze (voltage lead wire) turns to be very small,
where the absolute TEP value of phosphor-bronze wire is much less than 0.5
V/K below 80 K. For copper and platinum wires measured against to the
phosphor-bronze wire, the agreement between measured results and the literature
data is good. To demonstrate the applied magnetic field response of the system,
we report measurements of the TEP on single crystal samples of LaAgSb and
CeAgSb in fields up to 140 kOe.Comment: 10 pages, 8 figures. accepted in Measurement Science and Technolog
Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication
Anisotropic determined up to 92 T and the signature of multi-band superconductivity in Ca(PtAs)((FePt)As) superconductor
The upper critical fields, (), of single crystals of the
superconductor
Ca(PtAs)((FePt)As)
( 0.246) are determined over a wide range of temperatures
down to = 1.42 K and magnetic fields of up to 92 T. The
measurements of anisotropic () curves are performed in pulsed
magnetic fields using radio-frequency contactless penetration depth
measurements for magnetic field applied both parallel and perpendicular to the
\textbf{ab}-plane. Whereas a clear upward curvature in
() along \textbf{H}\textbf{c} is
observed with decreasing temperature, the ()
along \textbf{H}\textbf{ab} shows a flattening at low temperatures.
The rapid increase of the () at low
temperatures suggests that the superconductivity can be described by two
dominating bands. The anisotropy parameter,
, is 7 close
to and decreases considerably to 1 with decreasing temperature,
showing rather weak anisotropy at low temperatures.Comment: 4pages, 3figures, accepted PRB Rapid Communicatio
Hydrostatic pressure study of single-crystalline UNi0.5Sb2
We studied single-crystals of the antiferromagnetic compound UNi0.5Sb2 (TN ~
161 K) by means of measurements of magnetic susceptibility (chi), specific heat
(Cp), and electrical resistivity (rho) at ambient pressure, and resistivity
under hydrostatic pressures up to 20 kbar, in the temperature range from 1.9 to
300 K. The thermal coefficient of the electrical resistivity (drho/dT) changes
drastically from positive below TN to negative above, reflecting the loss of
spin-disorder scattering in the ordered phase. Two small features in the rho vs
T data centered near 40 and 85 K correlate well in temperature with features in
the magnetic susceptibility and are consistent with other data in the
literature. These features are quite hysteretic in temperature, i.e., the
difference between the warming and cooling cycles are about 10 and 6 K,
respectively. The effect of pressure is to raise TN at the approximate rate of
0.76 K/kbar, while progressively suppressing the amplitude of the small
features in rho vs T at lower temperatures and increasing the thermal
hysteresis.Comment: 9 pages, 3 figues, 2007-mmm conferenc