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Structural and transport properties of epitaxial Fe/ZnSe/FeCo magnetic tunnel junctions
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
2001 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 18, 184422- p.Article in journal (Refereed) Published
Abstract [en]

The use of a semiconductor barrier in heteroepitaxy with ferromagnetic metal electrodes describes a novel type of magnetic tunnel junctions. In this work, epitaxial Fe/ZnSe/FeCo magnetic tunnel junctions have been grown on ZnSe(001) buffered GaAs(001) substrates by molecular beam epitaxy. Alloying a small amount of Co with Fe in the base electrode provides a better seed epilayer for the growth of the ZnSe barrier compared to pure Fe as seen by transmission electron microscopy. Detailed characterization of the FeCo surface was performed by in situ scanning tunneling microscopy and revealed pyramid-shaped defects of up to 60 Å in height distributed on the FeCo surface. Transport measurements on microfabricated tunnel junctions yielded up to 16% magnetoresistance at 10 K and the effect is attributed to spin polarized tunneling across the semiconductor barrier in the energy range of the gap. The observed anomalous character of the magnetoresistance was attributed to conduction through the pyramidal defects in the base FeCo layer.

Place, publisher, year, edition, pages
2001. Vol. 64, no 18, 184422- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-89806DOI: 10.1103/PhysRevB.64.184422OAI: oai:DiVA.org:uu-89806DiVA: diva2:161585
Available from: 2002-04-25 Created: 2002-04-25 Last updated: 2013-06-13Bibliographically approved
In thesis
1. Properties of Fe/ZnSe Heterostructures: A Step Towards Semiconductor Spintronics
Open this publication in new window or tab >>Properties of Fe/ZnSe Heterostructures: A Step Towards Semiconductor Spintronics
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis, the properties at ferromagnet/semiconductor interfaces, relevant for semiconductor spintronics applications, are addressed. Semiconductor spintronics refers to the possibility of storing information using the electron spin, additional to the electron charge, for enhanced flexibility in nanoscale semiconductor devices.

The system under focus is the Fe/ZnSe(001) heterostructure, where ZnSe is a wide gap semiconductor ideally compatible with GaAs. The heterostructures are grown on GaAs(001) substrates by molecular beam epitaxy. From various electron-beam based diffraction, spectroscopy and microscopy techniques, it is shown that Fe grows epitaxially and predominantly in a layer-by-layer mode on ZnSe(001) with no presence of chemically reacted phases or interdiffusion.

An in-plane uniaxial magnetic anisotropy (UMA) is detected for thin Fe films on ZnSe(001) by magnetometry, thus opposing the cubic symmetry of bcc Fe. From first principles calculations, the unidirectional sp3-bonds from ZnSe are shown to induce this uniaxiality. Moreover, an in-plane anisotropic lattice relaxation of Fe is found experimentally, seemingly as a consequence of the sp3-bonds, giving an additional UMA contribution via magneto-elastic coupling. It is proposed that these two effects are responsible for the much-debated UMA observed in Fe/semiconductor structures in general.

The interface magnetism is probed by x-ray magnetic circular dichroism and Mössbauer spectroscopy. It is found that the magnetic moment at the interface is comparable or even enhanced with respect to the bulk Fe. These two experiments are believed to provide the first unambiguous proof of a persistent bulk magnetic moment at a transition metal/semiconductor interface.

Spin-polarised transport measurements are performed on Fe/ZnSe/FeCo magnetic tunnel junctions. A magnetoresistance of 16% is found at low temperature, which evidences both the existence of interface spin polarisation, as inferred from the bulk magnetic moment above, and that the spin polarisation can be transmitted across the semiconductor barrier layer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2002. 55 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 713
Keyword
Physics, semiconductor spintronics Fe ZnSe heterostructures spin injection interface magnetism magnetic tunnel junctions, Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-1983 (URN)91-554-5314-7 (ISBN)
Public defence
2002-05-24, Siegbahnsalen, Uppsala, 10:15 (English)
Opponent
Available from: 2002-04-25 Created: 2002-04-25 Last updated: 2012-04-04Bibliographically approved

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