• R. Laiho
  • K. G. Lisunov
  • E. Lähderanta
  • V. N. Stamov
  • V. S. Zakhvalinskii
  • A. I. Kurbakov
  • A. E. Sokolov

The thermopower, S, of La0.7Ca0.3Mn1-yFeyO3 (y = 0-0.09), measured for T = 25-310 K and magnetic fields of B = 0-10 T, exhibits strong sensitivity to doping with Fe. The weak increase of S observed in the undoped material with lowering temperature is enhanced considerably in the sample with y = 0.03 until a steep decrease takes place in the vicinity of the paramagnetic-ferromagnetic transition temperature, TC. S increases with further growth of y and its maximum follows the decrease of TC from 228 K at y = 0.03 to 119 K at y = 0.09. Application of a magnetic field reduces S strongly. The experimental data are analysed quantitatively with a percolation model using results of our recent investigations of the Shklovskii-Efros-like variable-range hopping conductivity in the same set of La1-xCaxMn1-yFeyO3 samples with evidence for a soft Coulomb gap and a rigid gap in the density of states near the Fermi level (Laiho et al 2002 J. Phys.: Condens. Matter 14 8043). In the paramagnetic insulating phase the temperature dependence of S is determined by competing contributions from two types of asymmetry of the gap: a small shift of its centre with respect to the Fermi level and cubic non-parabolicity. Numerical values of the shift and the cubic asymmetry terms are determined.

Original languageEnglish
Pages (from-to)881-890
Number of pages10
JournalJournal of Physics Condensed Matter
Volume16
Issue number6
DOIs
StatePublished - 18 Feb 2004

    Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

ID: 99520407