A1 Journal article (refereed), original research

Assymmetry of a complex gap near the Fermi level, determined from measurements of the thermopower in La1-xCaxMn1-yFeyO3


Publication Details

Authors: Laiho P, Lisunov K G, Lähderanta Erkki, Stamov V, Zakhvalinskii V, Kurbakov AI, Sokolov A E

Publisher: IOP Publishing: Hybrid Open Access

Publication year: 2004

Language: English

Related journal or series: Journal of Physics: Condensed Matter

Volume number: 16

Issue number: 6

Start page: 881

End page: 890

Number of pages: 10

ISSN: 0953-8984

eISSN: 1361-648X

JUFO level of this publication: 0

Digital Object Identifier (DOI): http://dx.doi.org/10.1088/0953-8984/16/6/016

Open Access: Not an Open Access publication


Abstract

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, T-C. S
increases with further growth of y and its maximum follows the decrease
of T-C 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.


Last updated on 2019-30-09 at 13:29