Etude par diffraction de neutrons de la phase Sr 0,5La 1,5Li 0,5Fe 0,5O 4

A neutron diffraction study has been carried out on Sr _0.5La _1.5Li _0.5Fe _0.5O ₄ of K ₂NiF ₄-type derived structure and it has shown that iron in the tetravalent state has a high spin configuration ( t³_2ge¹_g) and that the material has some stacking defects. At room temperature this compound shows an ordering between iron and lithium atoms leading to a nuclear cell a₀√2, a₀√2, c₀ ( a₀ and c₀ are the parameters of the K ₂NiF ₄-type cell). At low temperature ( T < {T _N}/{2}) the magnetic structure can be described as antiferromagnetic, corresponding likely to a colinear pattern with a propagation vector of 0.5 ( {2π}/{a ₀}) along the [110] axis. At higher temperature ( {T _N}/{2} < T < T _N) helimagnetic structure is consistent with a propagation vector of 0.47 ( {2π}/{a ₀}) [110].