engleski

Microwave investigations of ruthenate-cuprates

In the last few years, the class of copper oxide superconductors with ruthenium content has been intensively investigated. A number of studies reported the intriguing coexistence of superconductivity and magnetic order in RuSr2R2Cu2O10 and RuSr2RCu2O8 where R=Gd or Eu. Most recent reports have focused on RuSr2GdCu2O8, which has a unit cell similar to that of the YBa2Cu3O7 high temperature superconducting cuprate (HTSC) with two CuO2 layers and one RuO2 layer in a unit cell. There exists a magnetic ordering transition at a temperature Tm, greater than the superconducting transition temperature, Tc. According to several studies, there is a competition between ferromagnetic and antiferromagnetic ordering on a microscopic scale. This generated considerable interest because ferromagnetic order and superconductivity are competing processes and can only coexist via some accommodation, for example by a spatial modulation of the respective order parameters or the formation of a spontaneous vortex phase. We have preformed a series of microwave measurements on these samples combined with several other experimental methods on the same samples. Microwave measurements on sintered ceramic samples and powdered samples dispered in epoxy resin have proven to be very useful to distinguish intrinsic (intragranular) properties of the compound from the (mostly semiconducting) properties of intergranular regions.[1] Furthermore, we have clearly shown that the conduction occurs through RuO2 planes as well as through the CuO2 planes. However, below the superconducting transition temperature, the considerable microwave absorption indicates that RuO2 planes remain normal. Comprehensive measurements of dc and ac susceptibility, dc resistance, magnetoresistance, Hall resistivity, and microwave absorption and dispersion in fields up to 8 T provided experimental evidence in support of theoretical models which base the coexistence of superconductivity and magnetic order on decoupled CuO2 and RuO2 planes.[2] References: [1] M. Požek, A. Dulčić, D. Paar, G. V. M. Williams, and S. Krämer, Phys. Rev. B 64, 064508 (2001). [2] M. Požek, A. Dulčić, D. Paar, A. Hamzić, M. Basletić, E. Tafra, G. V. M. Williams, and S. Krämer, Phys. Rev. B 65, 174514 (2002).

superconductivity; magnetism; ruthenocuprates; microwaves

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