LOW FIELD MAGNETORESISTIVE BEHAVIOUR OF La1..A.Mn03 (A=Sr, Ca) AND Sr2FeMo06 PEROVSKITES

Abstract

The discovery of negative magnetoresistance (MR) properties in manganese perovskite has demonstrated for the second time after the break through about high Tc superconducting cuprates that oxides offer a very promising field for the investigation of new materials with specific properties susceptible to be involved in device applications. In 1994, S. Jin et al observed about thousand-fold change in resistance in the epitaxial thin film of perovskite La2/3Ca1i3Mn03 at a high magnetic field of 6 tesla and this extremely large change in resistance was epitomized by the name "Colossal magnetoresistance (CMR)". After that, perovskite manganites with mixed valence of manganese, R14A„Mn03 (R is a rare earth such I#4kit41 Baa L%A 4_etctayebeen the subject of great interest for the scientific community because of colossal magnetoresistance (CMR). These doped perovskite manganites show the simultaneous appearance of metal to insulator and ferromagnetic to paramagnetic transition. From a fundamental point of view the CMR effect seems to be closely related to the donftiteeliditimitostraiMe proposed by de Gennes and Goodenough. Nevertheless recent studies made by Millis suggest that Jahn-Teller type electron phonon interactions are greatly involved in the appearance of such properties. Clearly, the knowledge of the crystal structure and chemical bonding of these compounds is of prime importance to understand the CMR properties of these compounds. The interest in these systems exists not only due to their application in magnetic recording/memories, magnetic switches, bolometric detectors etc but due to various interesting properties e.g. charge, orbital, spin ordering and spin-dependent tunneling exhibited by them