Enhancements of magnetoresistance in Bi- or Ti-doped La0.67Ba0.33MnO3

Magnetic and transport properties for the series of (La0.67Ba0.33MnO3)/(Bi2O3)x/2 and (La0.67Ba0.33MnO3)/(TiO2)x have been studied. The doping Bi almost has no influence on the magnetization M and Curie temperature Tc, but remarkably improves the low-field magnetoresistance at low temperature. On the contrary, doping Ti depresses (M) and lowers Tc and peak resistivity temperature Tp, accompanying the rapid increase in the resistivity, and increases the high-field magnetoresistance at low temperature obviously. Different physical mechanisms are discussed for these different behaviors. The surface state of the particles is a key factor influencing on the magnetoresistance effects. Small amount addition of Bi or Ti can improve the room temperature magnetoresistance obviously. These results are favorable for the application studies.