Synthesis, Computations and Characterizations of Low Dimensional Rare-Earth Compounds

Reduced rare-earth (Ln, lanthanide elements) compounds with low-dimensional Ln-Ln-bonded structures are promising candidates for magnetic materials because Ln-Ln-bonded molecules and solids have delocalized 5d electrons that make strong magnetic coupling possible. Four new rare-earth compounds were synthesized in this work, I. Gd_(9)Br_(16)O_(4), II. Gd_(6)Br_(7)Si_(2), III. Pr_(3)Si and IV. Pr_(2)I_(2)Ge. The first two gadolinium bromide compounds exhibit 1-dimensional Ln-Ln-bonded motifs imbedded within layered structures. Pr_(3)Si is a new binary phase with a structure that can be more easily visualized by focusing on the interpenetrating (10, 3)-a silicon network. Pr_(2)I_(2)Ge has a double-layered structure. The results of EHTB band structure calculations indicate that the bottom the Gd_(9)Br_(16)O_(4) d bands and those of a hypothetical analogous yttrium compound (Y_(9)Br_(16)O_(4)) are half filled; the Fermi levels of those two compounds cut through two d bands. Gd_(6)Br_(7)Si_(2) and Pr_(3)Si are predicted to be metallic, as expected. The results of magnetic measurements on Gd_(6)Br_(7)Si_(2) show that it behaves like a soft magnet at 2 K and undergoes phase transitions at 27 K and 70 K.