Magnetic ordering in the layered oxyselenides Sr2CoO2Ag2Se2 and Ba2CoO2Ag2Se2

Synthesis, Structure, and Compositional Tuning of the Layered Oxide Tellurides Sr2MnO2Cu2–xTe2 and Sr2CoO2Cu2Te2

“…The magnetic susceptibility ( Figure 9) showed a broad maximum centered at around 270 K, with a peak in the first derivative d(χT)/dT, which we equate to T N , at 180(20) K. These features are typical for two-dimensional systems. 6,31,32 The observed T N is too high for Curie or Weiss constants to be extracted from this temperature regime.…”

“…As discussed above, in the context of the manganese analogue, the large telluride ion distorts the chalcogenide layers significantly away from the ideal tetrahedral angle in the cobalt analogue. 6,19 Magnetic Properties. Magnetic Ordering in Sr 2 MnO 2 Cu 2−x Te 2 Phases.…”

“…The temperature dependence of the intensity of the magnetic Bragg peaks gives an estimate for T N of 175(5) K, consistent with our interpretation that the maximum in the derivative of the magnetic susceptibility (Figure 9) corresponds to the long-range ordering, and the broad susceptibility maximum above this temperature arises from short-range correlations that precede long-range order on further cooling. 6 Smura et al 5 noted that the orbital contribution in an octahedral Co 2+ environment (such as in CoO) 34 is significant, but it is quenched on mild distortions from this environment 35,36 (e.g., as in La 2 CoO 4 ). 37 However, significantly distending the CoO 4 S 2 octahedron causes the ordered moment to recover, and the total moment exceeds that of CoO when the coordination environment approaches square planar.…”

“…Ordered magnetic moment of Co 2+ as a function of the coordination geometry for a series of compounds with distended octahedral CoO 4 X 2 environments (X = halide or chalcogenide). 5,6,38 The Co−X distances have been normalized (see text) to take account of the different radii of the anions. Figure 13.…”

Orbital Magnetic Moments of the High-Spin Co2+ Ions at Axially-Elongated Octahedral Sites: Unquenched as Reported from Experiment or Quenched as Predicted by Theory?

“…For a series of magnetic solids made up of axially elongated CoO 4 X 2 (X = Cl, Br, S, Se) octahedra containing high-spin Co 2+ (d 7 , S = 3 / 2 ) cations, interesting magnetic properties were found by Knee and Weller, by Smura et al, and by Herkelrath et al: (a) The magnetic moments of the Co 2+ ions are considerably greater than the spin moment of 3 μ B , namely, 3.22 μ B for Sr 2 CoO 2 Cl 2 , 3.52 μ B for Sr 2 CoO 2 Br 2 , 3.7 μ B for Sr 2 CoO 2 Ag 2 Se 2 , 3.81 μ B for Sr 2 CoO 2 Cu 2 S 2 , 3.97 μ B for Ba 2 CoO 2 Ag 2 Se 2 , and 4.45 μ B for Ba 2 CoO 2 Cu 2 S 2 . (b) The total moments μ tot of these ions increase almost linearly with the bond length ratio, R = r Co–X / r Co–O (Figure ).…”