Publication highlights

1.
A. K. Paul, M. Reehuis, V. Ksenofontov, B. H. Yan, A. Hoser, D. M. Többens, P. M. Abdala, P. Adler, Martin Jansen, and C. Felser, "Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6," Physical Review Letters 111, 1-5 (2013).

Double perovskites

Magnetization and neutron diffraction studies revealed that the double perovskite Sr2FeOsO6 features two magnetic phase transitions leading to magnetic phases AF1 and AF2, respectively. This is also evident from the Mössbauer spectra of Sr2FeOsO6 [1] (Fig. 1). The isomer shifts are typical for Fe3+ for all the spectra which excludes that charge fluctuations are associated with the magnetic transitions. Above the Néel temperature the Mössbauer spectra show a slightly broadened single line, in agreement with the nearly undistorted FeO6 units in the crystal structure. Below TN = 140 K the appearance of a hyperfine sextet confirms the evolution of magnetic order. However, in the whole temperature range of the existence of the AF1 magnetic phase the lines are broad which suggests the persistence of a considerable degree of disorder. Furthermore, the average hyperfine fields Bhf increase very gradually and do not reach the typical values of Fe3+ (t2g3eg2) compounds (Bhf ~ 50 T). Below 67 K a second six-line pattern with increased Bhf gains intensity at the expense of the first sextet with decreasing temperature. Finally, at 5 K a single quite sharp six-line pattern with  Bhf = 49 T verifies full local ordering of the Fe3+ magnetic moments in the AF2 phase. The trends in Bhf (Fig. 1b) are fully consistent with the evolution of the magnetic moments derived from the neutron diffraction study.

<strong>Figure</strong> <strong>1</strong> (from Ref. [1]): M&ouml;ssbauer spectra of Sr<sub>2</sub>FeOsO<sub>6</sub> at the indicated temperatures. (b) Temperature dependence of the average magnetic hyperfine fields B<sub>hf</sub>. (c) Hyperfine field distributions at 60 and 90 K. (d) Temperature dependence of the magnetic susceptibility in a field of 0.01 T. Zoom Image
Figure 1 (from Ref. [1]): Mössbauer spectra of Sr2FeOsO6 at the indicated temperatures. (b) Temperature dependence of the average magnetic hyperfine fields Bhf. (c) Hyperfine field distributions at 60 and 90 K. (d) Temperature dependence of the magnetic susceptibility in a field of 0.01 T. [less]
 
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