Evolution of the hyperfine parameters of Fe in superconducting LiFeAs as observed by 57Fe Mössbauer spectroscopy

The LiFeAs superconductor is studied by 57Fe Mössbauer spectroscopy to detect possible changes in the hyperfine parameters in terms of temperature upon passing the superconductivity-transition-temperature at ∼16 K. With decreasing temperature, a rather fast growth of spectral area and isomer shift below TcTc, peaking at ∼6 K was seen. This indicates an increase in the stiffness of the lattice followed by softening.