Low field magnetoresistance and conduction noise in La0.67Ba0.33 MnO3 film

Screen printed polycrystalline films of La 0 . 6 7 Ba 0 . 3 3 MnO 3 (LBMO) have been found to exhibit larger magnetoresistance at low field and low temperature as compared to an epitaxial LBMO film prepared by laser ablation technique. A value of magnetoresistance ratio (MRR) of 6% has been achieved even at a dc field of 600 Oe at 77 K. Temperature dependence of MRR of the screen printed film shows that MRR increases with the decrease of the temperature. This MRR-T behavior shows that the magnetoresistance in screen printed film has its origin in grain boundaries. The variation of MRR of these films with-magnetic field at 77 K shows sharp increase in the field 0 to 1 kOe and slower increase for the field 1 to 3 kOe. Sharp increase in the MRR has been attributed to spin polarized tunneling across the grain boundaries where as the slower increase in MRR for a field variation of 1 to 3 kOe is due to suppression of spin disorders present at the grain boundary region in the polycrystalline LBMO films. Conduction noise of polycrystalline film is measured and compared with the conduction noise of epitaxial LBMO film and conduction noise in epitaxial LBMO film with single bicrystal grain boundary.