Berlin 2005 – scientific programme

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MA: Magnetismus

MA 18: Magnetische dünne Schichten III

MA 18.10: Talk

Monday, March 7, 2005, 12:45–13:00, TU H1028

Strain and disorder effects on the transport properties of manganite thin films — •Carmine Antonio Perroni, Vittorio Cataudella, Giulio De Filippis, and Vincenzo Marigliano Ramaglia — Dipartimento Scienze Fisiche, Universita’ "Federico II", Napoli

Thickness dependence, strain and disorder effects in films of La_1−xA_xMnO₃ perovskites are analyzed in the colossal magnetoresistance regime. A reduction in the thickness of the film causes a decrease of critical temperature and an increase of resistivity at low temperatures. The strain effects are in good agreement with experimental data only if the dependence of the hopping matrix elements on the Mn-O-Mn bond angle is properly taken into account. In collaboration with experimental groups, the resistivity is investigated in a wide temperature range for films grown by different techniques and on several substrates allowing to analyze samples with different amounts of disorder. In the low-temperature state the prominent contribution to the resistivity scales as T^α with α ≃ 2.5 supporting the role of single magnon scattering in presence of minority spin states localized by the disorder. In the high temperature insulating paramagnetic phase the resistivity shows the activated behavior characteristic of polaronic carriers. Finally in the whole range of temperatures the experimental data are found to be consistent with a phase separation scenario also in films doped with strontium.