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Register a new userLong Range Antiferromagnetic Ordering in the S = 1/2 Ordered Rock Salt Oxide, Li5OsO6: Comparison with the Isoelectronicand Isostructural Spin Glass, Li4MgReO6
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Li5OsO6 and Li5ReO6 polycrystalline samples were synthesized by conventional solid state methods. Employing powder neutron diffraction data, the crystal structure of Li5OsO6 was re-investigated. Li5OsO6 crystallizes in C2/m space group in an ordered NaCl structure type where a = 5.0472(1) A, b = 8.7827(2) A, c = 5.0079(1) A, Beta = 109.777(2) degree and V = 208.90(1).A^3 Magnetic susceptibility and heat capacity data indicate an AFM long range order below 40K although there is evidence for low dimensional short range order above 80K. As well, the frustration index, f = |theta|/TN ~1, in contrast to the isostructural and isoelectronic compound, Li4MgReO6, which is a spin glass below 12K and has f ~ 14. An attempt was made to rationalize these differences using spin dimer analysis. The key results are that the spin exchange interactions in the Re-based compound are stronger and are consistent with a frustrated triangular lattice model while a low dimensional short range order model is better for Li5OsO6. The main reason for this is a strong Jahn-Teller distortion in the OsO6 octahedron material which constrains the unpaired electron to occupy the dxy orbital.
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The phase transition in the compound LiVGe2O6 has been proposed as a unique example of a spin-Peierls transition in an S=1 antiferromagnetic chain. We report neutron and x-ray diffraction measurements of LiVGe2O6 above and below the phase transition at T=24 K. No evidence is seen for any structural distortion associated with the transition. The neutron results indicate that the low temperature state is antiferromagnetic, driven by ferromagnetic interchain couplings.
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