Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 33: Postersession Correlated Electrons: Metal Insulator Transition, Spin Systems and Itinerant Magnets
TT 33.2: Poster
Mittwoch, 25. März 2009, 14:00–18:00, P1A
Thermodynamic 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 have investigated the magnetization M, specific heat cp and resistivity ρ of high-purity EuC2+x (-0.1≤ x ≤ 0.3) compounds. The magnetization of EuC2 shows a ferromagnetic ordering at TC ≃ 14K with a saturation moment of ≃ 7 µB/FE. This imply that EuC2 is composed of Eu2+ and the acetylide ion (C22−). TC hardly changes with x. 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 resistivity ρ over several orders of magnitude indicating a metal-insulator transition (MIT). Applying magnetic fields up to 14 tesla, we find a systematic shift of 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 magnetoresistance of the better known 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.