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Transport properties of the fully epitaxial Fe/O/MgO/Fe magnetic tunnel junctions : Influence of the interface (structural quality / pollution)

P.-J. Zermatten, SpinTech, Grenoble


P.-J. Zermatten1, F. Bonell2, G.Gaudin1, S. Andrieu2, C. Tiusan2, M. Chshiev1, A.Schuhl1

1SpinTec, CEA/CNRS/UJF/INPG, Grenoble, France

2Nanomagnetism and Spintronics Team, Institut Jean Lamour (UMR 7198 CNRS – Nancy Université), Vandoeuvre-lès-Nancy, France

 

Magnetic tunnel junctions (MTJs) benefit of a strong scientific interest [1] motivated both by their high potential for applications in sensor and storage devices and by the complex fundamental physics of spin dependent tunnelling. Theoretical models of tunnelling in single crystal devices [2–4] have been successfully confronted to experimental observations of tunnelling magnetoresistance (TMR) in single-crystal MTJs involving a MgO tunnel barrier [5,6]. In these systems, the TMR effects are determined by the different tunneling mechanisms and symmetry-related decay rates of the Bloch waves for the majority and the minority spin channels within the barrier.
Moreover the electronic properties are highly sensitive to the crystalline structure and possible defects at the interfaces. For example, a two order of magnitude decrease of the transmission probability is expected when one monolayer of O is deposited between the ferromagnetic layer and the barrier [7].

 

In this seminar I will present the experimental evidence of the presence of two interfacial resonant states, located at the bottom Fe/MgO interface due to its high structural quality. Moreover, the influence of an additional O monolayer at the interface has been studied. To clearly study the role played by the Fe-O bonding at the interface without any consideration of the bulk Fe or MgO, we characterised couples of samples epitaxialy grown at the same time in a UHV chamber : Fe/MgO/Fe and Fe/O/MgO/Fe. All the electrical measurements have been performed using a modified atomic force microscope (AFM) where the full metal tip is contacted on nanopillars (down to 30x60 nm2).

 

1. W. J. Gallagher and S. S. P. Parkin, IBM J. Res. Dev. 50, 333 (2006).
2. W. H. Butler, et al., Phys. Rev. B 63, 054416 (2001).
3. X.-G. Zhang and W. H. Butler, J. Phys. : Condens. Matter 15, R1603 (2003).
4. J. Mathon and A. Umerski, Phys. Rev. B 63, 220403 (2001).
5. J. Faure-Vincent, et al., J. Appl. Phys. 93, 7519 (2003).
6. S. Yuasa, et al., Nat. Mater. 3, 868 (2004).
7. X.-G. Zhang et al., Phys. Rev. B 68 (2001) 092402.

 

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