Mössbauer studies of NaFes2 : magnetic hyperfine fields and covalency in MFeS2 compounds (m=Na, k, Rb, Cs)

Abstract

Mössbauer studies of NaFeS2 from room temperature down to liquid helium temperature indicate a magnetic ordering below 77 K. The magnitude of the hyperfine field is 270 kOe at 4.2 K. The measured hyperfine parameters characterize iron in NaFeS 2 to be in the high spin Fe3+ 6S5/2 configuration. We show that in NaFeS2 — as in the other MFeS 2 compounds (M=K, Rb, Cs) - the reduced values of hyperfine fields (150-270 kOe) can be correlated with simple concepts such as transferred hyperfine fields via 4s contribution and cationic electronegativity.