Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 5: Postersession Superconductivity: Materials - Fabrication and Properties
TT 5.30: Poster
Montag, 23. März 2009, 13:00–16:45, P1A
Thermal expansion studies on RFeAsO1−xFx (R=La, Ce, Pr, Sm, Gd) — •L. Wang, N. Leps, U. Köhler, G. Behr, R. Klingeler, C. Hess, and B. Büchner — Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Germany
We present thermal expansion α and magnetostriction data of RFeAsO1−xFx with R=La, Ce, Pr, Sm, Gd. The undoped compounds, with x=0, exhibit thermal expansion anomalies at both the spin ordering transition TN and the structural phase transition TS. A negative anomaly of α at TN clearly implies the negative pressure dependence of magnetic ordering. In addition, we find a large regime of structural fluctuations above TS which exhibit a positive pressure dependence. While no qualitative changes occur for different R-ions at higher temperature, the presence of magnetic R-sites yields antiferromagnetic order of 4f-moments. A finite magnetostriction far above the 4f-ordering temperatures indicates magnetic fluctuations. Upon doping, superconductivity evolves while both features indicating TN and TS disappear. The thermodynamic properties at the superconducting transitions are discussed.