Long Range Antiferromagnetic Ordering in the S = 1/2 Ordered Rock Salt Oxide, Li5OsO6: Comparison with the Isoelectronicand Isostructural Spin Glass, Li4MgReO6

TL;DR

This study reveals long-range antiferromagnetic order in Li5OsO6 with a frustrated triangular lattice, contrasting with the spin glass behavior of isostructural Li4MgReO6, due to differences in spin exchange interactions and Jahn-Teller distortions.

Contribution

The paper provides the first detailed structural and magnetic characterization of Li5OsO6, highlighting its long-range AFM order and contrasting it with the spin glass behavior of Li4MgReO6, and analyzes the underlying exchange interactions.

Findings

Li5OsO6 exhibits AFM long-range order below 40K.

Li4MgReO6 shows spin glass behavior below 12K.

Differences are due to stronger exchange interactions and Jahn-Teller effects in Li5OsO6.

Abstract

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.