Microstructural magnetic phases in superconducting FeTe_0.65Se_0.35

Abstract

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogenities in the iron chalcogenide system FeTe 1-x Se x and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe 0.65 Se 0.35 studied with transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate a presence of nanometre scale hexagonal regions coexisting with tetragonal host lattice, a chemical disorder demonstrating non homogeneous distribution of host atoms in the crystal lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe 3 O 4 inclusions and to hexagonal symmetry nanometre scale regions with structure of Fe 7 Se 8 type. Our results suggest that nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that faster grown crystal of inferior crystallographic properties is a better superconductor.

Anisotropy of the magnetic properties of the FeTe0.65Se0.35 superconductor

“…The jump is observed earlier by other researchers in much stronger fields and is associated with the presence of a magnetostructural transition in the layers of the magnetic impurity Fe 3 O 4 . 6 The difference in amplitude can be explained similar to the difference in the M f component in the total magnetization, as discussed above.…”

“…9 This deviation can be associated with the presence, and the spatial distribution, of magnetic inclusions in the superconducting sample, which exist in this compound and others like it. 10 These inclusions can be Fe 3 O 4 and Fe 7 Se 8 , 6 located in the interlayer space of the sample. As a result, the total magnetization of the sample M can be represented as two terms…”

Intrinsic pinning by naturally occurring correlated defects in FeSe1−xTexsuperconductors

“…In the XR diffraction patterns we identified the Fe 1-y Se (00l) and (l0l) families and the (00l) one for the a nanoscale intergrowth of both phases and its shape and size depends on the crystal growth parameters [6].…”

Dynamics of trapped magnetic flux in superconducting FeTe0.65Se0.35

“…X-ray studies have shown that the sample contains magnetite (Fe 3 O 4 ) impurity (less than 0.3 per cent of the sample mass), which can be responsible for the appearance of the feature observed in Fig. 2 at T = 120 К [7].…”