Etude des propriétés physiques des films de Fe3O4 épitaxiés et de la polarisation en spin à l'interface Fe3O4/γ-Al2O3

Abstract : Magnetite Fe3O4 is a promising material for spintronics since band structure calculations predict it to be half-metallic. One thus expect large magnetoresistance in magnetic tunnel junctions using Fe3O4 as electrode. We have grown 3 to 50 nm-thick Fe3O4 thin films onto sapphire by molecular beam epitaxy. The films are single crystalline but comprise a large number of antiphase boundaries. These defects are the origin of the magnetic anomalies of Fe3O4 thin films. which we qualitatively reproduiced
by using a one-dimensionnal model, the results being compared with the characteristic size of the antiphase boundaries measured by a fractal analysis. Moreover, the Verwey transition is not seen for thicknesses below 20 nm because of finite size effects; all samples show slow magnetization dynamics.

We have also developped a growth method allowing us to deposit γ-Al2O3 epitaxially onto Fe3O4 while controling the stoichiometry at the interface. Al2O3 thin films of thicknesses greater than 2 nm are continuous and allow magnetic decoupling between electrodes. Direct measurements by spin resolved photoemission yields to a -40 % the spin polarization at the Fe3O4/γ-Al2O3 interface whereas the tunnel magnetoresistance (reduiced by the magnetic disorder generated by the antiphase boundaries) is +3 % at 300 K for Fe3O4/γ-Al2O3/Co magnetic tunnel junctions.
Document type :
Theses
Condensed Matter [cond-mat]. Université Paris Sud - Paris XI, 2005. French


https://tel.archives-ouvertes.fr/tel-00085941
Contributor : Alexandre Bataille <>
Submitted on : Monday, July 17, 2006 - 1:30:42 PM
Last modification on : Friday, April 24, 2015 - 1:07:52 AM

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Alexandre Bataille. Etude des propriétés physiques des films de Fe3O4 épitaxiés et de la polarisation en spin à l'interface Fe3O4/γ-Al2O3. Condensed Matter [cond-mat]. Université Paris Sud - Paris XI, 2005. French. <tel-00085941>

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