Manganite-based magnetic tunnel junctions:: new ideas on spin-polarised tunnelling

The role played by the barrier in magnetic tunnel junctions is studied. We have prepared three types of junctions with the same ferromagnetic electrodes (La0.7Sr0.3MnO3 and Co) and three different insulating barriers (Al2O3, Ce1-xLaxO2-x/2, and SrTiO3). The tunnel magnetoresistance (TMR) is normal(resistance smaller in the parallel state) in the case of Al2O3 barrier while an inverse TMR effect (resistance smaller in the antiparallel state) is observed in the case of Ce1-xLaxO2-x/2 and SrTiO3 barriers. This emphasises that the barrier can change and even reverse the spin polarisation of Co by selecting the tunnelling electrons ("s" or "d" type). Implications of these novel results will be discussed. (C) 2000 Elsevier Science B.V. All rights reserved.