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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.50: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Low temperature behaviour of Sr and Ca doped manganites — •E. Forzani, V. Moshnyaga, and K. Winzer — I. Physikalisches Institut Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen

Perovskite manganites show insulator (I) to metal (M) phase transition, accompanied with a long range ferromagnetic ordering for doping level x ≥ 0.175. Recently it was argued [1] that electronic phase separation of IM-type can take place due to the competition of double- and superexchange interactions even for chemically homogeneous samples. To check for the possible phase separation and thus recovering of insulating behaviour (dρ /d T ≤ 0) at very low temperatures in the metallic samples, we studied single crystals and epitaxial films of Sr- and Ca-doped manganites. Measurements were carried out in a demagnetization cryostat for temperatures down to 40 mK and magnetic fields B = 0-7 T. As starting point, a La_1−xSr_xMnO₃ (x = 0.2) single crystal exhibits metallic behaviour of the resistivity ρ(T) for 4.2 K ≤ T ≤ 300 K. The high residual resistivity ratio RRR = 58 and temperature coefficient of resistivity TCR = 1/ρ (dρ /dT)≈ 13 %/K by the IM-transition at 305 K confirm the high crystal quality.

Göttingen Graduate School of Physics and DFG (SFB 602, TP A2) are acknowledged.

[1] E.Dagotto, T.Hotta, A.Moreo, Physics Reports 344,1 (2001)