Structural and magnetic properties of new rare-earth – antimony pyrochlore-type oxides Ln2BSbO7 (B = Sc, Ga, In)

A number of new quaternary rare-earth pyrochlores Ln2BSbO7 are reported with Ln = Pr, Nd, Eu, Gd or Dy, B = Sc, Ga or In. These compositions extend the range of available rare-earth pyrochlores with diamagnetic B-site cations, especially for early lanthanides (Pr, Nd). Rietveld refinements and Mössbauer spectroscopy show that most compounds actually contain a fraction of Sb3+, e.g. have a composition Ln2(B3+1−xSb3+xSb5+)O7. In addition, the rather large size of In3+ induces partial site exchange of Ln and In in Ln2InSbO7 phases. The cell parameters and interatomic distances are in good agreement with those in corresponding Ln2M4+2O7 pyrochlores. Magnetic measurements show dominant antiferromagnetic interactions and the absence of magnetic ordering down to 2 K, as expected in the geometrically frustrated lanthanide sublattice in the pyrochlore structure. Strong crystal field effects are present in all compounds excepted gadolinium ones. The europium magnetism (J = 0) is well described by a Van Vleck behaviour leading to a finite constant magnetic susceptibility at low temperature.

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