Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 32: Correlated Electrons: Poster Session
TT 32.35: Poster
Donnerstag, 28. Februar 2008, 14:00–18:00, Poster B
Magnetic and electrical properties of EuC2+x — •Oliver Heyer1, Derk Wandner2, Nils Hollmann1, Uwe Ruschewitz2, Thomas Lorenz1, and John A. Mydosh1 — 1II. Physikalisches Institut, Universiät zu Köln, D-50937 Köln — 2Institut für Anorganische Chemie, Universität zu Köln, D-50939 Köln
We present measurements of the magnetization M, specific heat cp and resistance ρ of EuC2+x (x=0, 0.1) compounds. The magnetization data show a ferromagnetic ordering at TC ≃ 14K with a saturation moment of ≃ 7 µB/FE. This suggests an oxidation state of Eu2+. In the paramagnetic phase all compounds are semiconductors with small bandgaps (10−20meV). A very interesting feature is that the onset of the ferromagnetic order decreases the resistance ρ over a couple of orders of magnitude indicating a metal-insulator transition (MIT). Moreover, an applied magnetic field shifts the MIT temperature to higher values, resulting in a colossal magnetoresistance with changes in the resistivity up to 6 orders of magnitude. This behaviour resembles the colossal magnetorsistance of the better known system of Eu-rich EuO. Furthermore we carried out magnetization and specific heat measurements of YbC2. The data identify this compound as a diamagnet without structural phase transitions. On this account YbC2 is used as a non magnetic reference system.