Superconductivity and Long-Range Magnetic Order in Ternary Rare Earth Iron Silicides

摘要

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 sub 2 Fe sub 3 Si sub 5 , Sc sub 2 Fe sub 3 Si sub 5 and Y sub 2 Fe sub 3 Si sub 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/sub 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 anonmalous properties of these materials. Low temperature heat capacity measurements on the compounds RE sub 2 Fe sub 3 Si sub 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 sub 2 Fe sub 3 Si sub 5 and Yb sub 2 Fe sub 3 Si sub 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 nonmagnetic divalent state. No evidence is found in the heat capacity data, even on careful inspection, for superconductivity in any of these antiferromagnetically ordered compounds. Anomalous behavior is observed with respect to spin wave and nuclear contributions to the total heat capacity, crystalline electric field effects and critical behavior including multiple magnetic phase transitions. (ERA citation 08:046747)