Novel ferromagnetism and negative magnetoresistance in BaBiO3 nanoparticles

Materials showing semiconducting and magnetic properties have significant commercial value presently, particularly in the field of spintronics. We report a novel ferromagnetic behavior and a negative magnetoresistance in the non-magnetic semiconductor perovskite material BaBiO3 at room temperature. We also observe an associated exchange spring like magnetic behavior in the sample annealed at a higher temperature. We discuss these effects based on a model of defect induced magnetic centers and magnetic domains in the material. The enhanced magnetization and exchange spring like behavior observed in the sample annealed at a higher temperature of 800 °C is attributed to higher number of magnetic defects and two dominant sizes of magnetic clusters. Photoluminescence and energy dispersive X-ray spectra corroborate the explanation based on charge induced defects in the material. Interplay of Bi3+ and Bi5+ states in BaBiO3, leads to a semiconducting behavior at room temperature. From the temperature dependence of the resistivity two distinct activation energies of 0.21 eV and 0.14 eV above and below 256 K, respectively, have been measured.