Structural chemistry and magnetic properties of Nd18Li8Fe4M'O39 (M'=Al, Ga) and La18Li8Fe4.5In0.5O39

Polycrystalline samples of Nd18Li8Fe4M'O39 (M'=Al, Ga) and La18Li8Fe4.5In0.5O39 have been prepared by the ceramic method and characterised by neutron diffraction and magnetometry. All three compounds adopt a cubic structure (space group Pm3[macr]n, a ~12 Aa) based on intersecting chains of cation sites with alternating octahedral and prismatic coordination geometry. These sites are occupied by Li, Fe and M' or In; Nd or La cations occupy sites between the chains. The cation distribution over the octahedral and prismatic sites within the chains is disordered in all three compounds. The Nd-containing compositions show spin-glass behaviour below ~4.5 K whereas small, weakly-ferrimagnetic domains form in La18Li8Fe4.5In0.5O39 below 7.60 K. The dependence of the magnetic properties on the nature of the lanthanide cation is discussed.