Study of low field magneto-resistance in La 0.67 A 0.33 MnO 3 [A ≡ Ca, Ba, Sr] screen printed films

Screen printed polycrystalline films of La 0 . 6 7 A 0 . 3 3 MnO 3 [A ≡ Ca, Ba, Sr] have been found to exhibit substantially large magneto-resistance at low fields and low temperature as compared to an epitaxial La 0 . 6 7 Ba 0 . 3 3 MnO 3 film prepared by laser ablation technique. A value of magneto-resistance 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 films show that MRR increases with decrease of the temperature. This MRR-T behaviour shows that magneto-resistance in screen printed films 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 0-1 kOe and slower increase for the field 1-3 kOe. Sharp increase in the MRR has been attributed to spin polarized tunnelling occurring across the grain boundaries, where as the slower increase in MRR for a field variation of 1-3 kOe is due to suppression of spin disorders present in the grain boundary region in the polycrystalline films.