Study of magnetransport properties in manganites with fixed structural parameters

Abstract

This work reports a detailed study of magnetic and transport properties of the manganite compounds ( R1, R2) 0.67( M1, M2) 0.33MnO 3 ( R1, R2=La, Gd, Pr, Tb, Ho; M1, M2=Ca, Sr, Ba). Taking into account that the ferromagnetic-to-paramagnetic and the metallic-to-semiconductor transition temperatures, as well as the magnetoresistance peak temperature, depend on the ionic radius of the A-site cations, 〈 r A 〉, as well as on the A-site ( A= R1, R2, M1 and M2) cationic size mismatch, σ 2( r A ), and also on the ratio Mn 3+/Mn 4+, compositions of the samples employed here were chosen to keep these parameters approximately constant. X-ray diffraction patterns indicate that all samples have similar structural characteristics. Experimental results show that they all present similar ferromagnetic–paramagnetic and metallic–semiconductor transition temperatures, as well as similar behavior of the magnetoresistance. We also found evidences of magnetic coupling between rare-earth and Mn moments at low temperatures, while at high temperatures the rare-earth ions have paramagnetic behavior. These results indicate that by controlling the structural parameters and preparation conditions, one can obtain samples with similar magnetic and electrical properties.