269 research outputs found
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
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
Thermal expansion of CaFe2As2: effect of cobalt doping and post-growth thermal treatment
We report thermal expansion measurements on Ca(Fe_(1-x)Co_x)_2As_2 single
crystals with different thermal treatment, with samples chosen to represent
four different ground states observed in this family. For all samples thermal
expansion is anisotropic with different signs of the in-plane and c-axis
thermal expansion coefficients in the high temperature, tetragonal phase. The
features in thermal expansion associated with the phase transitions are of
opposite signs as well, pointing to a different response of transition
temperatures to the in-plane and the c-axis stress. These features, and
consequently the inferred pressure derivatives, are very large, clearly and
substantially exceeding those in the Ba(Fe_(1-x)Co_x)_2As_2 family. For all
transitions the c-axis response is dominant
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