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

We report the results of investigation of high-temperature superconductor (HTSC) LaFeO F As at x = 0.15. We applied the XRD method, the measurement of the hysteresis curve and resistivity, as well as the Mössbauer measurements at the temperature range 4.2-300 K. We show that in the given sample, owing to doping by fluorine, full suppression of antiferromagnetism is not accompanied by the rise of superconductivity. Instead, we observe a high-temperature (at T ≤ 40 K) Kondo effect, which indicates a strong coupling of electron's spins with the magnetic moments of impurities. We also find a correlation between the revealed high-temperature Kondo effect and the appearance of a quadrupole splitting in the Mössbauer spectra below 40 K. The revealed effects can shed light on the mechanism of superconductivity in the iron-containing HTSC. [ABSTRACT FROM AUTHOR]