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Tunneling spectroscopy of magnetic double barrier junctions
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
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2007 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 6, 2818-2820 p.Article in journal (Refereed) Published
Abstract [en]

Scanning tunneling microscopy (STM) is used to study transport in magnetic double tunnel junctions (DTJs) formed using a fixed transparency barrier of a patterned tunnel junction (TJ), and a variable tunnel barrier between the top electrode of the patterned junction and the STM tip. A sufficiently thin top electrode has been predicted to result in a rectification of charge current through a DTJ when the two barriers have different transparency. Our measurements indeed show a high current rectification ratio for 3-nm-thick, continuous film top electrodes, which is observed for junctions with asymmetric tunnel barriers.

Place, publisher, year, edition, pages
2007. Vol. 43, no 6, 2818-2820 p.
Keyword [en]
current rectification, diode effect, magnetic tunnel junctions (MTJs), tunneling spectroscopy
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-39451DOI: 10.1109/TMAG.2007.893313ISI: 000246706200242Scopus ID: 2-s2.0-34249058694OAI: oai:DiVA.org:kth-39451DiVA: diva2:440069
Note
Conference: 10th Joint Magnetism and Magnetic Materials Conference/International Magnetics Conference. Balitmore, MD. JAN 07-11, 2007. QC 20110911Available from: 2011-09-12 Created: 2011-09-09 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Spin-diode effect and thermally controlled switching in magnetic spin-valves
Open this publication in new window or tab >>Spin-diode effect and thermally controlled switching in magnetic spin-valves
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis demonstrates two new device concepts that are based on the tunneling and giant magnetoresistance effects. The first is a semiconductor-free asymmetric magnetic double tunnel junction that is shown to work as a diode, while at the same time exhibiting a record high magnetoresistance. It is experimentally verified that a diode effect, with a rectification ratio of at least 100, can be obtained in this type of system, and that a negative magnetoresistance of nearly 4000% can be measured at low temperature. The large magnetoresistance is attributed to spin resonant tunneling, where the parallel and antiparallel orientation of the magnetic moments shifts the energy levels in the middle electrode, thereby changing their alignment with the conduction band in the outer electrodes. This resonant tunneling can be useful when scaling down magnetic random access memory; eliminating the need to use external diodes or transistors in series with each bit.

The second device concept is a thermally controlled spin-switch; a novel way to control the free-layer switching and magnetoresistance in spin-valves. By exchange coupling two ferromagnetic films through a weakly ferromagnetic Ni-Cu alloy, the coupling is controlled by changes in temperature. At room temperature, the alloy is weakly ferromagnetic and the two films are exchange coupled through the alloy. At a temperature higher than the Curie point, the alloy is paramagnetic and the two strongly ferromagnetic films decouple. Using this technique, the read out signal from a giant magnetoresistance element is controlled using both external heating and internal Joule heating. No degradation of device performance upon thermal cycling is observed. The change in temperature for a full free-layer reversal is shown to be 35 degrees Celsius for the present Ni-Cu alloy. It is predicted that this type of switching theoretically can lead to high frequency oscillations in current, voltage, and temperature, where the frequency is controlled by an external inductor or capacitor. This can prove to be useful for applications such as voltage controlled oscillators in, for example, frequency synthesizers and function generators. Several ways to optimize the thermally controlled spin switch are discussed and conceptually demonstrated with experiments.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 85 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:11
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-91300 (URN)978-91-7501-287-2 (ISBN)
Public defence
2012-03-30, FB52, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Supervisors
Note
QC 20120313Available from: 2012-03-13 Created: 2012-03-12 Last updated: 2012-03-13Bibliographically approved

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Haviland, David B.Korenivski, Vladislav

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