Condensed Matter Physics Seminar

NMR and Magnetization Studies of the Coexistence of Ferromagnetism and Superconductivity in RuSr2ReCu2O8 (Re = Eu, Gd)

Zhaohui Han
Department of Physics
University of Connecticut

Ferromagnetism and superconductivity are thought to be mutually exclusive since ferromagnetism lifts the degeneracy of the spin-up and spin-down electrons of a Cooper-pair (singlet, but not triplet). However, these two antagonistic phenomena are found to coexist in the newly discovered RuSr2ReCu2O8 (Re = Eu, Gd) system, so-called Re1212, which has a layered structure similar to that of YBa2Cu3O7-δ. Although it is believed that the magnetism is associated with the RuO2 layers, while the superconductivity is developed in the CuO2 layers, debates on some issues, such as the type of magnetic ordering, are still going on.

In order to gain insight into the coexistence of ferromagnetism and superconductivity in Re1212 (Re = Eu, Gd) microscopically, local studies using 99,101Ru spin-echo NMR and complimentary magnetization measurements have been carried out. Two distinct sets of 99,101Ru NMR signals are obtained at 1.3K. This result is discussed in terms of the microscopic magnetic structure, mixed valence states for Ru, and charge transfer. Magnetization measurements confirm the coexistence of superconductivity (30K and 28K for Gd1212 and Eu1212, respectively) and ferromagnetic-like ordering (130K and 132K for Gd1212 and Eu1212, respectively). Field dependence of the NMR also gives information on the type of magnetic structure.

Thursday, November 20, 2003
2:30 PM
Gant Science Complex
Physics Department
Room P121

(The seminar is followed by coffee/tea, cookies, and an informal discussions.)


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