Magnetism and mixed valence in some R<SUB>2</SUB>M<SUB>3</SUB>X<SUB>5</SUB> compounds: R = Ce, Eu, U; M = d metals, X = Si, Ge

The authors report new materials R<SUB>2</SUB>M<SUB>3</SUB>X<SUB>5</SUB> compounds mainly based on possible anomalous rare earths: Ce, Eu and actinide U. Lattice parameters, susceptibility and L<SUB>III</SUB> absorption edge versus temperature measurements have been performed on Ce, Eu based materials. Mossbauer experiments versus temperature are also reported on Eu<SUB>2</SUB>Ni<SUB>3</SUB>Si<SUB>5</SUB>. Magnetism is observed on Ce<SUB>2</SUB>Ir<SUB>3</SUB>Ge<SUB>5</SUB>, Eu<SUB>2</SUB>M<SUB>3</SUB>Si<SUB>5</SUB> (M=Cu, Pd) and U<SUB>2</SUB>Rh<SUB>3</SUB>Si<SUB>5</SUB>. New intermediate valence materials have been obtained in Ce<SUB>2</SUB>M<SUB>3</SUB>Si<SUB>5</SUB> (M=Rh, Ir), with a rather small deviation from the trivalent state of Ce ion. Eu<SUB>2</SUB>Ni<SUB>3</SUB>Si<SUB>5</SUB> is an intermediate valence compound. From Isomer Shift measurements and L<SUB>III</SUB> absorption edge measurements versus temperature the valence of Eu changes from #2.6 at 300K to #2.7 at 4.2K