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Register a new userElectrical Resistivity and Specific Heat of EuFe2As2 Single Crystals: Magnetic homologue of SrFe2As2
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We have grown single crystals of EuFe2As2 and investigated its electrical transport and thermodynamic properties. Electrical resistivity and specific heat measurements clearly establish the intrinsic nature of magnetic phase transitions at 20 K and 195 K. While the high temperature phase transition is associated with the itinerant moment of Fe, the low temperature phase transition is due to magnetic order of localized Eu-moments. Band structure calculations point out a very close similarity of the electronic structure with SrFe2As2. Magnetically, the Eu and Fe2As2 sublattice are nearly de-coupled.
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High-pressure electrical resistivity measurements up to 3.0GPa have been performed on EuFe2As2 single crystals with residual resistivity ratios RRR=7 and 15. At ambient pressure, a magnetic / structural transition related to FeAs-layers is observed at T0 =190K and 194K for samples with RRR=7 and 15, respectively. Application of hydrostatic pressure suppresses T0, and then induces similar superconducting behavior in the samples with different RRR values. However, the critical pressure 2.7GPa, where T0=0, for the samples with RRR=15 is slightly but distinctly larger than 2.5GPa for the samples with RRR=7.
Sn0.8Ag0.2Te is a new superconductor with Tc ~ 2.4 K. The superconducting properties of Sn0.8Ag0.2Te have been investigated by specific heat measurements under magnetic fields. Bulk nature of superconductivity was confirmed from the amplitude of the specific heat jump at the superconducting transition, and the amplitude is consistent with fully-gapped superconductivity. Upper critical field was estimated from specific heat and electrical resistivity measurements under magnetic fields. The Hall coefficient was positive, suggesting that the Ag acts as a p-type dopant in Sn0.8Ag0.2Te.
Low-temperature specific heat (SH) is measured for the 12442-type KCa$_2$Fe$_4$As$_4$F$_2$ single crystal under different magnetic fields. A clear SH jump with the height of $Delta C/T|_{T_c}$ = 130 mJ/mol K$^2$ is observed at the superconducting transition temperature $T_c$. It is found that the electronic SH coefficient $Deltagamma (H)$ quickly increases when the field is in the low-field region below 3 T and then considerably slows down the increase with a further increase in the field, which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s). The temperature-dependent SH data indicates the presence of the $T^2$ term, which supplies further information and supports the picture with a line-nodal gap structure. Moreover, the onset point of the SH transition remains almost unchanged under the field as high as 9 T, which is similar to that observed in cuprates, and placed this system in the middle between the BCS limit and the Bose-Einstein condensation.
Sizable single crystals of $BaFe_2As_2$ have been grown with self-flux method. The crystals are plate-like with c-axis perpendicular to the plane. The size can be as large as 3 x 5 x 0.2 $mm^3$. The resistivity anisotropy ($rho_c/rho_{ab}$) is as large as about 150, and independent of temperature. The transport in ab plane and along c-axis direction shares the same scattering mechanism. In contrast to the magnetic behavior of polycrystalline samples, no Curie-Weiss behavior are observed, a temperature linear dependent susceptibility occurs above spin-density-wave (SDW) transition. The susceptibility behavior is very similar to that of antiferromagnetic SDW chromium. Magnetic behavior of single crystal definitely gives evidence for existence of local moment except for the contribution to susceptibility from itinerant electrons. A resistivity minimum strongly dependent on magnetic field is observed. A log(1/T) divergency, similar to that of the underdoped cuprates, happens at low temperature. Here we first present intrinsic transport and magnetic properties, and their anisotropy from high quality single crystal.
Single crystals of SrFe2-xPtxAs2 (0 < x < 0.36) were grown using the self flux solution method and characterized using x-ray crystallography, electrical transport, magnetic susceptibility, and specific heat measurements. The magnetic/structural transition is suppressed with increasing Pt concentration, with superconductivity seen over the range 0.08 < x < 0.36 with a maximum transition temperature Tc of 16 K at x = 0.16. The shape of the phase diagram and the changes to the lattice parameters are similar to the effects of other group VIII elements Ni and Pd, however the higher transition temperature and extended range of superconductivity suggest some complexity beyond the simple electron counting picture that has been discussed thus far.
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