Study of low field magneto-resistance in La_0.67A_0.33MnO₃ [A ≡ Ca, Ba, Sr] screen printed films

Abstract

Screen printed polycrystalline films of La_0.67A_0.33MnO₃[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_0.67Ba_0.33MnO₃ 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.