Detailed physical property characterization of FeTe1-xSex x = 0.0 to 0.50 single crystals

TL;DR

This study synthesizes and characterizes FeTe1-xSex single crystals with x=0 to 0.50, revealing structural, magnetic, and superconducting properties, including phase transitions, superconductivity onset, and co-existing magnetism.

Contribution

It provides a comprehensive phase diagram and detailed physical property analysis of FeTe1-xSex crystals across the composition range, highlighting the interplay of magnetism and superconductivity.

Findings

Superconductivity observed at higher Se content with T_c up to 14K.

Magnetic and structural phase transitions are present at lower Se concentrations.

Coexistence of magnetism and superconductivity in certain compositions.

Abstract

Here, we report self flux single crystal growth of FeTe1-xSex for x = 0 to 0.50 series via solid state reaction route,the resulted crystals as seen are shiny. X Ray diffraction performed on the surface of crystals elucidated the growth in 00l plane, i.e. orientation in c direction only. Scanning electron microscopy (SEM) images showed slab like morphology and EDX (Energy dispersive X ray analyzer) confirmed that the crystals are closed to their designed compositions. Rietveld analysis of the XRD patterns of crushed crystal powders showed that the cell parameters decrease with Se content increase. Coupled magnetic and structural phase transition temperature, seen as a step in resistivity for the lower Se concentration and it is not detected for higher x values. Superconductivity is observed by resistivity measurement for higher Se concentration with a maximum temperature of 14K at x = 0.50. Thermally Activated Flux Flow (TAFF) analysis based on high field transport measurements in superconducting region done for x = 0.20 crystal. Raman spectroscopy at room temperature of synthesized samples exhibits all the allowed phonon modes with slight shift to higher frequency with Se content. Mossbauer spectra of FeTe1-xSex crystals series were recorded at 300 and 5K. At 5K, the average hyperfine field decreases systematically with Se content increase from 10.6 to 6.1Tesla for x = 0.0 to x = 0.20 samples. This indicates a possibility of co-existing magnetism and superconductivity in x = 0.07 to 0.20 crystals. For x = 0.50 sample, no hyperfine field related to magnetic ordering is seen. Based on above results, detailed phase diagram of the FeTe1-xSex compounds is defined in the present study.