A 57Fe M\"ossbauer Study Of Local Structure And Spin Arrangements In   Antiferromagnetic NaFeAs
  Detailed 57Fe M\"ossbauer spectroscopy measurements on superconducting NaFeAs powder crystals have been performed. The 57Fe spectra recorded in the paramagnetic temperature range (T > TN \approx 46 +/- 2 K) were discussed supposing Fe2+ ions are located in distorted tetrahedral (FeAs4) polyhedra. Our results reveal that the structural transition (TS \approx 55 K) has a weak effect on the electronic structure of iron atoms while the development of the antiferromagnetic order (T =< TN) induces a redistribution of the charge at 57Fe nuclei. In the low-temperature range, the spectra show a diffuse resonance absorption structure which evidences for the existence of a continuous distribution of hyperfine fields HFe at 57Fe nuclei. The shape of these spectra can be related to the formation of a microdomain structure or phase separation. Analysis of the resulting distributions p(HFe) has shown that the M\"ossbauer spectra give consistent and physically reasonable 57Fe hyperfine parameters over the whole temperature range. 
Igor Presniakov, Igor Morozov, Alexey Sobolev, Mariya Roslova,   Alexander Boltalin, Vladimir Son, Olga Volkova, Alexander V...
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el