Structural Chemistry and Magnetic Properties of Nd₁₈Li₈Fe₅O₃₉ and Nd₁₈Li₈Co₄O₃₉: the Interplay of Cation and Spin Ordering

Siân E. Dutton
Peter D. Battle
Fernande Grandjean, Missouri University of Science and Technology
Gary J. Long, Missouri University of Science and Technology
K. Oh-Ishi

This document has been relocated to http://scholarsmine.mst.edu/chem_facwork/2382

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Abstract

Polycrystalline samples of Nd₁₈Li₈Fe₅O₃₉ and Nd₁₈Li₈Co₄O₃₉ have been synthesized using a solid-state method and studied by a combination of neutron diffraction, direct and alternating current magnetometry, and, in the case of Nd₁₈Li₈Fe₅O₃₉, Mössbauer spectroscopy. Both compounds adopt a cubic structure (space group Pm3̅n, a₀ ~ 11.9 Å) based on intersecting (111) chains made up of alternating octahedral and trigonal-prismatic coordination sites. the Fe⁴⁺ cations in Nd₁₈Li₈Fe₅O₃₉ are found on only the smaller of the two distinct octahedral sites in the structure; Fe³⁺ and Li⁺ are disordered over the larger octahedral site and the trigonal-prismatic site. the Nd³⁺ cations occupy sites between the chains. the smaller octahedral site is fully occupied by cobalt in Nd₁₈Li₈Co₄O₃₉, with 25% of the larger octahedral sites being vacant; Li⁺ is only found on the prismatic sites. Nd₁₈Li₈Fe₅O₃₉ shows spin-glass-like behavior with a spin-freezing temperature of 5.75 K, whereas Nd₁₈Li₈Co₄O₃₉appears to order antiferromagnetically at 2.3 K. in both cases, the magnetic coupling involves the Nd³⁺ sublattice.