Exchange interactions, transition metal ions, chain

Bragg lines parallel to the c -axis in the neutron diffraction and the paramagnetic-like doublet of isolated T layers in the Mossbauer spectra of Lu2Fe307, at temperatures where spins on double T layers order, are a clear manifestation of a two-dimensionality of the spin correlation in these compounds. It is very likely that the rare earth elements in the U blocks couple weakly with transition metal ions on both sides of them and that the chain of the exchange interactions along the c-axis are cut at the U block. 

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