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

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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.