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Z. Shermadini

Publications and source records attributed to Z. Shermadini.

26 records · Page 2Linked to original sources
arXiv2011

Pressure cycle of superconducting Cs0.8Fe2Se2: a transport study

We report measurements of the temperature and pressure dependence of the electrical resistivity of single crystalline iron-based chalcogenide Cs0.8Fe2Se2. In this material superconductivity Tc~30K develops from a normal state with extremely large resistivity. At ambient pressure a large "hump" in the resistivity is observed around 200K. Under pressure, the resistivity decreases by two orders of magnitude, concomitant with a sudden Tc suppression around p~8GPa. Even at 9GPa a metallic resistivity state is not recovered, and the ρ(T) "hump" is still detected. A comparison of the data measured upon increasing and decreasing the external pressure leads us to suggest that superconductivity is not related to this hump.

cond-mat.supr-con↗
arXiv2011

Coexistence of Magnetism and Superconductivity in the Iron-based Compound Cs_0.8(FeSe_0.98)_2

We report on muon-spin rotation/relaxation (\muSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs_0.8(FeSe_0.98)_2. Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T_c = 28.5(2)K, the \muSR data indicate that the system is {\it magnetic} below T_N = 478.5(3)K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs_0.8(FeSe_0.98)_2 a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed ratio between T_N and T_c is the highest one reported to date for a magnetic superconductor.

cond-mat.supr-con↗
arXiv2011

Room temperature antiferromagnetic order in superconducting X_yFe_{2-x}Se_ 2, (X= Rb, K): a powder neutron diffraction study

Magnetic and crystal structures of superconducting X yFe 2-xSe 2 (X= Rb and K with Tc=31.5 K and 29.5 K) have been studied by neutron powder diffraction at room temperature. Both crystals show ordered iron vacancy pattern and the crystal structure is well described in the I4/m space group with the lattice constants a=8.799, c=14.576 and a=8.730, c=14.115 A, and the refined stoichiometry x=0.30(1), y=0.83(2) and x=0.34(1), y=0.83(1) for Rb- and K-crystals respectively. The structure contains one fully occupied iron position and one almost empty vacancy position. Assuming that the iron moment is ordered only on the fully occupied site we have sorted out all eight irreducible representations (irreps) for the propagation vector k=0 and have found that irreps tau_2 and tau_7 well fit the experimental data with the moments along c-axis. The moment amplitudes amounted to 2.15(3) mu_B, 2.55(3) mu_B for tau_2 and 2.08(6) mu_B, 2.57(3) mu_B for tau_7 for Rb- and K-crystals respectively. Irrep tau_2 corresponds to the Shubnikov group I4/m' and gives a constant moment antiferromagnetic configuration, whereas tau_7 does not have Shubnikov counterpart and allows two different magnetic moments in the structure.

cond-mat.str-el↗
arXiv2011

Iron vacancy superstructure and possible room temperature antiferromagnetic order in superconducting Cs_{y}Fe_{2-x}Se_2

Neutron and x-ray powder and single crystal synchrotron diffraction of CsyFe2-xSe2 show the presence of superstructure reflections with propagation vector k=[2/5, 1/5, 1] with respect to the average crystal structure I4/mmm (a = 4, c = 15A). The propagation vector star corresponds to the 5 times bigger unit cell given by transformation A=2a+b, B= -a+2b, C= c. A solution for the atomic structure is found in the space groups P42/n and I4/m with an ordered pattern of iron vacancies corresponding to the iron deficiency x = 0.29 and Cs stoichiometry y = 0.83. The superstructure satellites are more pronounced in the neutron diffraction patterns suggesting that they can have some magnetic contribution. We have sorted out possible symmetry adapted magnetic configurations and found that the presence of AFM ordering with the ordered magnetic moment of Fe with 2μB does not contradict to the experimental data. However, the solutions space is highly degenerate and we cannot choose a specific solution. Instead we propose possible magnetic configurations with the Fe magnetic moments in (ab)-plane or along c-axis. The superstructure is destroyed above Ts ~ 500 K by a first-order-like transition.

cond-mat.other↗
arXiv2010

Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27K

We report on the synthesis of large single crystals of a new FeSe-layer superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron powder-diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of the recently discovered potassium intercalated system KxFe2Se2. The new compound Cs0.8(FeSe0.98)2 shows a slightly lower superconducting transition temperature (Tc=27.4 K) in comparison to 29.5 in K0.8(FeSe0.98)2). The volume of the crystal unit cell increases by replacing K by Cs - the c-parameter grows from 14.1353(13) Å to 15.2846(11) Å. For the so far known alkali metal intercalated layered compounds (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2) the Tc dependence on the anion height (distance between Fe-layers and Se-layers) was found to be analogous to those reported for As-containing Fe-superconductors and Fe(Se1-xChx), where Ch=Te, S.

cond-mat.supr-con↗
arXiv2010

Microscopic Study of the Superconducting State of the Iron Pnictide RbFe_2As_2

A study of the temperature and field dependence of the penetration depth λof the superconductor RbFe_2As_2 (T_c=2.52 K) was carried out by means of muon-spin rotation measurements. In addition to the zero temperature value of the penetration depth λ(0)=267(5) nm, a determination of the upper critical field B_c2(0)=2.6(2) T was obtained. The temperature dependence of the superconducting carrier concentration is discussed within the framework of a multi-gap scenario. Compared to the other "122" systems which exhibit much higher Fermi level, a strong reduction of the large gap BCS ratio 2Δ/k_B T_c is observed. This is interpreted as a consequence of the absence of interband processes. Indications of possible pair-breaking effect are also discussed.

cond-mat.supr-con↗
arXiv2007

Influence of pulsed magnetic field on single- and two-pulse nuclear spin echoes in multidomain magnets

By the method of additional pulsed magnetic field influence in different magnetic materials (half metals, manganites, lithium ferrite, cobalt) it is established the analogy of time diagrams of magnetic pulse influence on single- and two pulse echoes in magnets when the distortion mechanism of single-pulse echo formation is effective, and the absence of such analogy in the case of lithium ferrite where the multipulse mechanism of single-pulse echo formation is effective. It is shown also that the timing and frequency diagrams of magnetic pulse influence on the two-pulse echo signals, corresponding to the symmetric and asymmetric magnetic pulse applications in the studied magnets, are defined by their domain walls parameters and could serve for their qualitative and quantitative characterization.

cond-mat.mtrl-sci↗