Ferromagnetic insulating and spin glass properties of La0.7Sr0.3MnO3–TiO2 composites

Abstract

In this study, the effect of TiO2 doping on the electro-magnetic properties of (1−x)La0.7Sr0.3MnO3+xTiO2 (with 0%≤x≤6%, in wt%) composites has been investigated. X-ray diffraction observations show the evidence of reaction between the La0.7Sr0.3MnO3 and TiO2 grains. Also the results show that by increasing TiO2 doping levels, the metal insulator transition temperatures decrease and the system becomes an insulator. Furthermore, the paramagnetic–ferromagnetic transition temperature also decreases as TiO2 content increases. The spin glass state exists in the composites with x=5% and 6%. The dynamic properties of the magnetic properties are investigated by temperature dependence of dc magnetization and frequency dependence of ac susceptibilities. A dynamic scaling analysis of ac susceptibility data using conventional critical slowing down indicates that a finite spin-glass phase-transition temperature (Tg) and a dynamic exponent (zv) change from 103K and 9.30 correspondingly for 0.95La0.7Sr0.3MnO3/0.05TiO2 to 133K and 9.10, for 0.94La0.7Sr0.3MnO3/0.06TiO2. In addition, MR in low temperature of these samples decline simultaneously with occur spin-glass behavior. These results are interpreted as the dilution of Mn3+/Mn4+ interactions by the random Ti substitution on the Mn site considerably reduces the ferromagnetic double exchange interaction within the manganese lattice.