The field of spintronics is concerned with the search for highly spin-polarized materials, such as transition metal oxide based half-metals. The electronic structure of transition metal oxides is not well understood yet because 3d electrons are strongly correlated and cannot be adequately described within a standard band theory framework. There is also a lack of experimental results proving the true half-metallic behaviour.
We present ARPES and SP-ARPES studies of monocrystalline Fe3O4(100) / MgO(100) and La0.7Sr0.3MnO3(100) / SrTiO3(100) films. The absence of the quasiparticle close to the Fermi energy observed for both systems disagrees with band calculations, but can be explained by strong electron-lattice coupling. This coupling modifies also the spin polarisation at the Fermi level. Simulations of the spectre taking into account the k broadening and initial-state lifetime broadening, have allowed us to reconcile the ARPES data with the bulk band structure calculated within the LDA+U framework. In particular, the spin-resolved data are consistent with the half-metallic nature of both oxides.
LPMS, Université de Cergy-Pontoise – LENSIS/SPCSI, CEA