Influence of magnetic tunnel barriers on magneto resistance behavior

Abstract : The presentation will begin by a short introduction to the magnetoresistance phenomenon and its applications. After that, I will talk about the effects of replacing non-magnetic tunnel barriers in tunnel type magnetoresistance materials with magnetic tunnel barriers. I will mainly focus on the results obtained by us in La0.67Sr0.33MnO3 – CoFe2O4 powder composite and Fe3O4 – CoFe2O4 core-shell systems. Our experimental investigations into these composite systems establish that the magnetoresistance of the composite material systems can be effectively manipulated by controlling the magnetic state of the tunnel barrier (CoFe2O4 in the present case). It will also be shown that in case of powder composites the magnetoresistance behaviour can be qualitatively altered leading to inversion of the resistance – field curves with respect to field direction. We explain this unconventional behaviour by considering the effects of dipolar magnetic coupling between La0.67Sr0.33MnO3 and CoFe2O4. On the other hand, the magnetoresistance in the core-shell system is influenced by a strong interface exchange coupling.