Spin polarised tunnelling as a probe of half metallic ferromagnetism in mixed-valence manganites

We report on spin-dependent tunneling measurements in all-oxide spin valves in which mixed valence manganites La0.7Sr0.3MnO3 electrodes are separated by a thin insulating layer. Information about the density of states and pol arisation properties of LaSrMnO can be inferred from the variations of the differential conductance with applied voltage and magnetic field. Our measu rements are consistent with the existence of a 1.5 eV wide e(g) band almost fully polarised at the Fermi level. High levels of spin polarisation lead to a large magnetoresistance at low fields and a high-field contribution is attributed to the presence of canted interfacial manganite phases. A low-f ield magnetoresistance ratio of 450% below 100 Oe was obtained on a sample with a SrTiO3 barrier, indicating a spin polarisation value in excess of 0. 83 for the manganite. (C) 1999 Published by Elsevier Science B.V. All right s reserved.