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Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
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2019 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 126, no 7, article id 075305Article in journal (Refereed) Published
Abstract [en]

The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.

Place, publisher, year, edition, pages
2019. Vol. 126, no 7, article id 075305
National Category
Condensed Matter Physics
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URN: urn:nbn:se:uu:diva-394269DOI: 10.1063/1.5089556ISI: 000483849000004OAI: oai:DiVA.org:uu-394269DiVA, id: diva2:1359382
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved

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Pálsson, Gunnar K.Moubah, RedaHjörvarsson, Björgvin

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