Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Physics and Astronomy


A systematic study of the superconducting and magnetic properties at low temperatures of some ternary rare-earth iron silicides is reported. Low temperature heat capacity measurements on three superconducting ternary rare-earth iron silicides, Lu(,2)Fe(,3)Si(,5), Sc(,2)Fe(,3)Si(,5) and Y(,2)Fe(,3)Si(,5), indicate a number of unusual features in the superconducting state of these materials. These materials show a large linear term in the superconducting heat capacity and a reduced normalized jump in the specific heat at T(,c). These data suggest a significant fraction of the conduction electrons in these materials do not participate in the superconducting state but instead remain "normal" well below the superconducting transition temperature. A two band model is proposed to explain these and previously reported anomalous properties of these materials;Low temperature heat capacity measurements on the compounds^RE(,2)Fe(,3)Si(,5), RE=Sm, Gd-Yb, from 0.5 K to 30 K confirm previously^reported antiferromagnetic ordering temperatures for RE=Gd-Tm^and indicate that the compounds Sm(,2)Fe(,3)Si(,5) and Yb(,2)Fe(,3)Si(,5) also^order antiferromagnetically. The magnetic behavior of Yb in this^system is consistent with lattice parameter determinations which^indicate Yb is in the trivalent state rather than the more usual non-^magnetic divalent state. No evidence is found in the heat capacity^data, even on careful inspection, for superconductivity in any ofthese antiferromagnetically ordered compounds. Anomalousbehavior is observed with respect to spin wave and nuclearcontributions to the total heat capacity, crystalline electric field;effects and critical behavior including multiple magnetic phase transitions; *DOE Report IS-T-1053. This work was performed under contractNo. W-7405-Eng-82 with the U.S. Department of Energy.



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Cronin Beals Vining



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104 pages