Adler, P.; Ksenofontov, V.; Paul, A.K.; Reehuis, M.; Yan, B.; Jansen, M.; Felser, C.: Magnetic phase transitions and iron valence in the double perovskite Sr2FeOsO6. Hyperfine Interactions 226 (2014), p. 289-297
10.1007/s10751-013-0922-6

Abstract:
The insulating and antiferromagnetic double perovskite Sr2FeOsO6 has been studied by 57Fe Mössbauer spectroscopy between 5 and 295 K. The iron atoms are essentially in the Fe3+ high spin (t2g3eg2) and thus the osmium atoms in the Os5+ (t2g3) state. Two magnetic phase transitions, which according to neutron diffraction studies occur below TN = 140 K and T2 = 67 K, give rise to magnetic hyperfine patterns, which differ considerably in the hyperfine fields and thus, in the corresponding ordered magnetic moments. The evolution of hyperfine field distributions, average values of the hyperfine fields, and magnetic moments with temperature suggests that the magnetic state formed below TN is strongly frustrated. The frustration is released by a magneto-structural transition which below T2 leads to a different spin sequence along the c-direction of the tetragonal crystal structure.