Mössbauer Investigation of Superconductors LaFeO 0.85F 0.15As and High-Temperature Kondo Effect

Mössbauer Study of Superconductors LaFeO0.88F0.12As

“…At the same time, in Mössbauer measurements, we observed the modification of a local structure of LaFeO 0.85 F 15 As at the temperatures below 40 K, which leads to the transformation of a single resonant line to a doublet line with the value of quadrupole splitting equal to 1.10 mm/s [1].…”

“…Like in the previous study [1], the LaFeAsO 0.88 F 0.12 samples have been manufactured in the form of toroid with an external diameter of 12 mm, internal diameter of 9.5 mm, and a height of 5 mm. The powder samples of LaFeAsO 0.88 F 0.12 used for XRD and Mössbauer measurements have also been prepared.…”

“…In our previous paper [1], we presented the results of investigation of a high-temperature superconductor of LaFeO (1−x) F x As type at x = 0.15, applying X-ray diffraction (XRD) method, Mössbauer spectroscopy, as well as magnetic and electric measurements in a wide temperature range of 4.2-300 K. We did not observe a superconductivity in the sample up to T = 4.2 K. Instead, below 40 K, we revealed the high-temperature Kondo effect (i.e., the inverse dependence of resistivity on the temperature), which could indicate a strong coupling of electron spins with magnetic moments of impurities [2]. At the same time, in Mössbauer measurements, we observed the modification of a local structure of LaFeO 0.85 F 15 As at the temperatures below 40 K, which leads to the transformation of a single resonant line to a doublet line with the value of quadrupole splitting equal to 1.10 mm/s [1].…”

“…Nov. Magnetism 27, 1825, 2014, where the high-temperature Kondo effect had been observed in the sample with x = 0.15. We proceed with exploring the properties of the LaFeO 0.88 F 0.12 As sample, applying the X-ray diffraction (XRD) method, resistivity measurement, and the magnetic and Mössbauer measurements at the temperature range of 4.2-300 K. We observe the emergence of high-temperature Kondo effect at the temperatures between 30 and 50 K. At the same time, as opposed to the case x = 0.15, we reveal the transformation of the high-temperature Kondo effect to the high-temperature superconductivity at the temperature near 25 K. The Mössbauer spectra of the sample obtained at different temperatures represent a single line, lying near zero relative velocity and do not exhibit any visible alterations.…”

“…In order to explain the emergence of superconductivity, a spin fluctuation model resulting from Fermi surface nesting between hole and electron pockets based on a density of functional theory calculations has been proposed [5,6]. The previous results [1] suggest that the interaction between electron spins and magnetic moments of impurities has been caused by fluorine doping.…”