Structural chemistry and magnetic properties of Nd18Li8Fe5O39 and Nd18Li8Co4O39: the interplay of cation and spin ordering.
Polycrystalline samples of Nd(18)Li(8)Fe(5)O(39) and Nd(18)Li(8)Co(4)O(39) 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 Nd(18)Li(8)Fe(5)O(39), Mossbauer spectroscopy. Both compounds adopt a cubic structure (space group Pm3n, a(0) approximately 11.9 A) based on intersecting 111 chains made up of alternating octahedral and trigonal-prismatic coordination sites. The Fe(4+) cations in Nd(18)Li(8)Fe(5)O(39) are found on only the smaller of the two distinct octahedral sites in the structure; Fe(3+) and Li(+) are disordered over the larger octahedral site and the trigonal-prismatic site. The Nd(3+) cations occupy sites between the chains. The smaller octahedral site is fully occupied by cobalt in Nd(18)Li(8)Co(4)O(39), with 25% of the larger octahedral sites being vacant; Li(+) is only found on the prismatic sites. Nd(18)Li(8)Fe(5)O(39) shows spin-glass-like behavior with a spin-freezing temperature of 5.75 K, whereas Nd(18)Li(8)Co(4)O(39) appears to order antiferromagnetically at 2.3 K. In both cases, the magnetic coupling involves the Nd(3+) sublattice.
Dutton
Siân E
SE
Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK.
Battle
Peter D
PD
Grandjean
Fernande
F
Long
Gary J
GJ
Oh-Ishi
Katsuyoshi
K