Structure, magnetic, magnetocaloric and magnetoresistance properties of La1-xPbxMnO3 perovskite

Abstract

La1-xPbxMnO3 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) perovskites were prepared by a solid-state reaction. Except for x = 0.5 (cubic) and x = 0.4 (rhombohedral), the structure of the other compositions was pseudo-rhombohedral with P1 symmetry. The particle size of the grains is depending on the Pb content of the samples. The Curie temperature Tc increases from 235 K for x = 0.1-310 K for x = 0.2 and is almost constant (about 360 K) for x ≥ 0.3. The field-cooled and zero-field-cooled thermomagnetic curves measured at low field show a split below a so-called irreversibility temperature Tr, which is somewhat smaller than Tc except for x = 0.1, where it is 270 K. From a series of magnetic isotherms the magnetic entropy changes δS(T) were determined for a field step of 500 Oe. The maximum value of δSmax increases with increasing x till x = 0.3 and then decreases with further increasing x. The conductivity of perovskites is metallic at low temperatures and semiconducting at high temperatures. Magnetoresistance measurements have been performed. © 2002 Elsevier Science B.V. All rights reserved.