798 research outputs found
MgB2 thick film with TC = 40.2 K deposited on sapphire substrate
We have successfully deposited thick MgB2 film on the (0001) crystalline
surface of sapphire by the method of hybrid physical-chemical vapor deposition
(HPCVD). The film thickness is about 1.3 micron. It has a dense and interlaced
structure. The film surface, shown by SEM, is stacked with MgB2 microcrystals.
Transport measurements by the 4-probe technique have demonstrated that its
critical temperature is about 40.2 K, with a sharp transition width of 0.15 K.
The residual resistivity ratio (RRR) is about 11. By extrapolation, HC2(0) is
determined as 13.7 T from the magneto-transport measurement. Also by hysteresis
measurement and applying the Bean model, the critical current density is
estimated as 5*1010 A/m2 in zero magnetic field. The present work has
demonstrated that HPCVD is an effective technique to fabricate the MgB2 thick
film with decent superconducting properties. Hence, it is important for the
future superconducting application, in particular, as a crucial preliminary
stage to fabricate superconducting tape.Comment: 7 pages with 4 figures included, Phys. Stat. Sol. (a) In pres
Preserved entropy and fragile magnetism
A large swath of strongly correlated electron systems can be associated with
the phenomena of preserved entropy and fragile magnetism. In this overview we
present our thoughts and plans for the discovery and development of lanthanide
and transition metal based, strongly correlated systems that are revealed by
suppressed, fragile magnetism or grow out of preserved entropy. We will present
and discuss current examples such as YbBiPt, YbAgGe, YbFe2Zn20, PrAg2In,
BaFe2As2, CaFe2As2, LaCrSb3 and LaCrGe3 as part of our motivation and to
provide illustrative examples
Combined effects of pressure and Ru substitution on BaFe2As2
The ab-plane resistivity of Ba(Fe1-xRux)2As2 (x = 0.00, 0.09, 0.16, 0.21, and
0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order
to explore the T-P phase diagram and to compare the combined effects of
iso-electronic Ru substitution and pressure. The parent compound BaFe2As2
exhibits a structural/magnetic phase transition near 134 K. At ambient
pressure, progressively increasing Ru concentration suppresses this phase
transition to lower temperatures at the approximate rate of ~5 K/% Ru and is
correlated with the emergence of superconductivity. By applying pressure to
this system, a similar behavior is seen for each concentration: the
structural/magnetic phase transition is further suppressed and
superconductivity induced and ultimately, for larger x Ru and P, suppressed. A
detailed comparison of the T-P phase diagrams for all Ru concentrations shows
that 3 GPa of pressure is roughly equivalent to 10% Ru substitution.
Furthermore, due to the sensitivity of Ba(Fe1-xRux)2As2 to pressure conditions,
the melting of the liquid media, 4 : 6 light mineral oil : n-pentane and 1 : 1
iso-pentane : n-pentane, used in this study could be readily seen in the
resistivity measurements. This feature was used to determine the freezing
curves for these media and infer their room temperature, hydrostatic limits:
3.5 and 6.5 GPa, respectively.Comment: 27 pages, 19 figure
Specific heat jump at the superconducting transition temperature in Ba(Fe(1-x)Cox)2As2 and Ba(Fe(1-x)Nix)2As2 single crystals
We present detailed heat capacity measurements for Ba(Fe(1-x)Cox)2As2 and
Ba(Fe(1-x)Nix)2As2 single crystals in the vicinity of the superconducting
transitions. The specific heat jump at the superconducting transition
temperature (Tc), Delta Cp/Tc, changes by a factor ~ 10 across these series.
The Delta Cp/T$ vs. Tc data of this work (together with the literature data for
Ba(Fe0.939Co0.061)2As2, (Ba0.55K0.45)Fe2As2, and (Ba0.6K0.4)Fe2As2) scale well
to a single log-log plot over two orders of magnitude in Delta Cp/Tc and over
about an order of magnitude in Tc, giving Delta Cp/Tc ~ Tc^2
Anisotropic thermal expansion of AEFe2As2 (AE = Ba, Sr, Ca) single crystals
We report anisotropic thermal expansion of the parent, AEFe2As2 (AE = Ba, Sr,
and Ca), compounds. Above the structural/antiferromagnetic phase transition
anisotropy of the thermal expansion coefficients is observed, with the
coefficient along the a-axis being significantly smaller than the coefficient
for the c-axis. The high temperature (200 K < T < 300 K) coefficients
themselves have similar values for the compounds studied. The sharp anomalies
associated with the structural/antiferromagnetic phase transitions are clearly
seen in the thermal expansion measurements. For all three pure compounds the
"average" a-value increases and the c-lattice parameter decreases on warming
through the transition with the smallest change in the lattice parameters
observed for SrFe2As2. The data are in general agreement with the literature
data from X-ray and neutron diffraction experiments
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