Mixed state properties of iron based Fe(Se,Te) superconductor fabricated by Bridgman and by self-flux methods

Abstract

The superconducting and transport properties of iron based Fe(Se,Te) superconductors fabricated by means of Bridgman (B) and Self-flux (S) methods have been compared using dc Magnetization (M) measurements as a function of temperature (T) and magnetic field (H). The M(T) measurements performed in Zero Field Cooling-Field Cooling conditions show higher critical temperature Tc and a lower spurious magnetic background signal for the sample (B) rather than the (S) one. By considering the superconducting M(H) hysteresis loops, the sample (B) shows a stronger superconducting signal together with the presence of a peak effect. The field and temperature dependence of the critical current densities Jc are extracted from the superconducting hysteresis loops M(H) within the Bean critical state model, and the high ratio between the JcB and the JcS, relative to the two typologies of samples, together with the comparison between their upper critical field Hc2, points out that the Bridgman method is most attractive for exploiting superconducting and transport properties in view of applications.

A precursor mechanism triggering the second magnetization peak phenomenon in superconducting materials

“…We have analyzed a FeSe 0.5 Te 0.5 (nominal composition) crystal with dimensions 3 × 3 × 0.2 mm 3 , produced by means of Bridgman technique and having T c = 14.5 K. Fabrication details are reported elsewhere 44 . A SEM–EDX analysis performed on the sample has shown the presence of twin boundaries and a slight deviation of the stoichiometry (Fe 0.96 Te 0.59 Se 0.45 ) from the nominal composition 72 . This is probably due to micro inhomogeneity and phase separation of magnetic premises, typical for the crystal growth and synthesis in FeSeTe 73 – 76 and its basic compound FeSe 77 , 78 .…”

High Pinning Force Values of a Fe(Se, Te) Single Crystal Presenting a Second Magnetization Peak Phenomenon

“…In fact, the IBSs showed low anisotropy values [2][3][4][5][6][7] and a preferable superconductor-normal-superconductor (SNS) behavior of the grain boundary junctions [8][9][10]. Despite their low T c values, it has been demonstrated that the IBSs can be suitable for magnet and wire production and/or highpower applications and high-current transport thanks to their high values of critical current density J c , irreversibility field and upper critical field [11][12][13][14][15][16] as well as their good inter-grain connectivity [8,13,17,18]. Among the various IBS families, the 11 family has attracted a lot of interest due to its very simple crystalline structure and to the possibility of easily doping it with several elements of the periodic table [19][20][21][22][23] in order to improve the superconducting properties of the compounds.…”

The Effect of Hydrogenation on Structure and Superconducting Properties of FeTe0.65Se0.35 Single Crystals

“…3a) with respect to the H-axis, which indicates the possible influence of the Bean-Levingston surface barrier, the presence of an uncompensated magnetic moment of Fe ions, as well as other Fe-based inclusions. [21][22][23][24] The impact of an uncompensated magnetic moment of Fe ions and/or other Fe-based inclusions on the shape of hysteresis loop in the studied materials seems to be dominant. The asymmetry of the loop for the sample hydrogenated at 250 o C is significantly reduced as compared to that one for the as-grown sample and for the samples hydrogenated at 180 and compound 19 In consequence, superconducting properties: critical temperature as well as capability to carry the superconducting current are much poorer.…”

“…In the case of the FeTe 0.65 Se 0.35 crystal, one should take into account the presence of excess Fe, as well as magnetic inclusions such as Fe 3 O 4 and Fe 7 Se 8 , which are located in the interlayer space of the superconductor and on its surface. [22][23][24] As a result, the magnetization of sample, M, is a superposition of two contributions M ≈ M F + M D , where M F and M D are the ferromagnetic and diamagnetic contributions, respectively. As a result, the magnetization loop M(H) becomes asymmetric (Fig.…”