title: Mössbauer study of superconducting NdFeAsO(0.88)F(0.12) and its parent compound NdFeAsO.
abstract: (57)Fe Mössbauer spectroscopy has been used to investigate the magnetic order of non-superconducting NdFeAsO (T(N) = 140 K) and superconducting NdFeAsO(0.88)F(0.12) (T(c) = 45 K). A magnetic hyperfine field B(hf) was observed at the (57)Fe nucleus below T(N)∼140 K for NdFeAsO. Below ∼2 K an increase of B(hf) relative to the saturation value was attributed to the transferred B(hf) at the Fe site resulting from the collinear antiferromagnetic (AF) spin structure of the Nd moments. The analysis of the spectra is consistent with a commensurate AF order of Fe spins. No  B(hf) is observed in superconducting NdFeAsO(0.88)F(0.12) down to 1.5 K.
authors.affiliation: Instituto de Física, Universidade Federal Fluminense, Avenida Milton Tavares de Souza, s/n-Campus da Praia Vermelha, 24210-346 Niterói, RJ, Brazil.
authors.forename: D R
authors.initials: DR
authors.lastname: Sánchez
authors.forename: M
authors.initials: M
authors.lastname: Alzamora
authors.forename: J
authors.initials: J
authors.lastname: Munevar
authors.forename: N L
authors.initials: NL
authors.lastname: Wang
authors.forename: G F
authors.initials: GF
authors.lastname: Cheng
authors.forename: E
authors.initials: E
authors.lastname: Baggio-Saitovitch