7th INTERNATIONAL CONFERENCE ON FERRITES

J. Phys. IV France 07 (1997) C1-635-C1-636
DOI: 10.1051/jp4:19971262

Thermal Properties of Some RE_1-xEA_xMnO₃ Compounds

J. Liebe¹, E. Kraus¹, L. Haupt¹, K. Bärner¹, P. Mandal², I.V. Medvedeva³, E. Gmelin⁴ and R.v. Helmolt<sup>5

1</sup>  IV. Phys. Institute, University of Göttingen, Bunsenstr. 11-15, 37073 Göttingen, Germany
²  Saha Institute of Nuclear Physics, 1-AF Bidhannagar, Calcutta, 700064, India
³  Institute for Metal Physics, Kovalevskaya Str. 18, 620219, Ekaterinburg, Russia
⁴  Max-Planck-Insitut für Festkörperforschung, Postfach 800665, 70506 Stuttgart, Germany
⁵  Siemens AG, Corporate Research and Development, P.O. Box 3220, 91050 Erlangen, Germany

Abstract
The Seebeck- effect and the thermal diffusivity K of epitaxial layers of La_0.67Ca_0.33Mn_3-δ and bulk samples of Nd_0.67Sr_0.33Mn_6-δ were investigated in the temperature range 35<K<300K using the time resolved thermoelectric power (flash) method. In the temperature regime of the high magnetoresistance (GMR) which is close to the maximum resistivity ρ_max of the La-Ca compound, we find a sign change of S(T) and a step in heat conductivity which we attribute to a temperature - induced metal-insulator transition at about 80K. For Nd_0.67Sr_0.33Mn_6-δ such a transition is also observed, but around 160K ; here S(T) is always positive except for a gradua1 sign change at 370 K and the changes in K are also more gradual. For temperatures above ρ_max we find evidence of a spin glass like state in both cases.

© EDP Sciences 1997