Magnetic phase transitions and iron valence in the double perovskite Sr 2 FeOsO 6
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Magnetic phase transitions and iron valence in the double perovskite Sr2 FeOsO6 Peter Adler · Vadim Ksenofontov · Avijit Kumar Paul · Manfred Reehuis · Binghai Yan · Martin Jansen · Claudia Felser
© Springer Science+Business Media Dordrecht 2013
Abstract The insulating and antiferromagnetic double perovskite Sr2 FeOsO6 has been studied by 57 Fe Mössbauer spectroscopy between 5 and 295 K. The iron atoms are essentially in the Fe3+ high spin (t2g 3 eg 2 ) and thus the osmium atoms in the Os5+ (t2g 3 ) 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. Keywords Double perovskites · Magnetic properties · Spin frustration · 57-iron Mössbauer spectroscopy
Proceedings of the 32nd International Conference on the Applications of the Mössbauer Effect (ICAME 2013) held in Opatija, Croatia, 1–6 September 2013. P. Adler (B) · A. K. Paul · B. Yan · M. Jansen · C. Felser Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany e-mail: [email protected] V. Ksenofontov · C. Felser Institut für Anorganische Chemie, Johannes Gutenberg-Universität, 55128 Mainz, Germany A. K. Paul · M. Jansen Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany M. Reehuis Helmholtz-Zentrum für Materialien und Energie, 14109 Berlin, Germany
P. Adler et al.
1 Introduction Since the discovery of large tunnelling magnetoresistance (TMR) effects in the half-metallic ferromagnetic double perovskites Sr2 FeMoO6 [1] and Sr2 FeReO6 [2] there has been renewed interest in the magnetic and electronic properties of other transition metal (TM) double perovskites with the general formula A2 BB’O6 . In the double perovskite structure the TM sites are atomically ordered and every B site is connected via the intervening oxygen atoms only with B’ sites and vice versa. In particular materials with a combination of an electronically strongly correlated 3d element on theB and a weaker correlated 4d or 5d element on the B’ site may allow a tuning of properties via adjustment of interactions like double-exchange, superexchange, and spin-orbit coupling. For iron-based double perovskites the availability of 57 Fe Mössbauer spectroscopy is particularly appealing as it is a sensitive probe for the local magnetic order, the valence states of iron, structural distortions and antisite disorder which is frequently present in such materials. Recently we have synthesized Sr2 FeOsO6 which crystallizes in the tetragonal space group I4/m and is an antiferromagnet
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