Münster 1999 – wissenschaftliches Programm

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AM: Magnetismus

AM 10: Postersitzung

AM 10.44: Poster

Dienstag, 23. März 1999, 16:15–20:00, F\"urstenberghaus

Magnetic inhomogeniety in perovskite manganites La_0.7Ca_0.3Mn_1−x(Fe/Ge)_xO₃ — •E. Gmelin¹, G.H. Rao^1,2,3, J.R. Sun³, E. Schmitt¹, N. Hamad², L. Haupt², and K. Bärner² — ¹MPI für Festköperforschung, Heisenbergstr.1, D-70569 Stuttgart, Germany — ²IV. Physikalisches Institut der Universität Göttingen,Bunsenstr. 11–15, D–37073, Göttingen, Germany — ³Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080, P.R. China

Hole doped perovskite rare earth manganese oxides exhibit attractive colossal magnetoresistance (CMR) effects. However, efforts to understand the intrinsic properties of these materials are often hindered by the presence of microscopic inhomogenieties, which are also of concern for the technological applications of the materials. To study the correlation between the microscopic inhomogeneities and the CMR properties, two series of compounds La_0.7Ca_0.3Mn_1−xFe_xO₃ and La_0.7Ca_0.3Mn_1−xGe_xO₃ (0≤ x ≤ 0.1) are prepared from different starting materials. Magnetisation, resistivity and specific heat of the compounds are investigated between 77K and 300K. Preliminary experimental results indicate that the doping of Fe or Ge on Mn sites do not alter the structural symmetry of the parent compound, but result in a reduction of the magnetisation, an increase of the resistivity, a decrease of the magnetic and metal–isulator transition temperatures. Magnetic inhomogeneity in the compounds are evidenced by the prominent broadening of the magnetic transition indicated in the temperature dependence of magnetisation and specific heat. The magnetic inhomogeineity probably originates from an inhomogeneous distribution of oxygen or cation vacancies. The effects of sample preparation conditions and a correlation between entropy of magnetic transition and Curie temperature are discussed.