Long-range antiferromagnetic ordering in the S=1/2 ordered rocksalt oxide Li_5OsO_6: Comparison with the isoelectronic and isostructural spin glass Li_4MgReO_6
Li_5OsO_6 and Li_5ReO_6 polycrystalline samples were synthesized by conventional solid state methods. Employing powder neutron diffraction data, the crystal structure of Li-5OsO_6 was reinvestigated. Li_5OsO_6 crystallizes in C2/m in an ordered NaCl structure type, where a=5.0472(1) A, 6=8.7827(2) A, c=5.0079(1) A, β=109.777(2)° and V=208.90(1) A~3. Magnetic susceptibility and heat capacity data indicate an antiferromagnetic long-range order below 40 K, although there is evidence for low dimensional short-range order below 80 K. As well, the frustration index, f= θ/T_N~ 1, in contrast to the isostructural and isoelectronic compound, Li_4MgReO_6, which is a spin glass below 12 K 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 Li_5OsO_6. The main reason for this is a strong Jahn-Teller distortion in the OsO_6 octahedron material which constrains the unpaired electron to occupy the d_(xy) orbital.
展开▼
