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Exchange-induced phase separation in Ni-Cu films
Institute of Magnetism, National Academy of Sciences of Ukraine.
Institute of Magnetism, National Academy of Sciences of Ukraine.
Institute of Magnetism, National Academy of Sciences of Ukraine.
Institute of Magnetism, National Academy of Sciences of Ukraine.
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2012 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 324, no 13, 2131-2135 p.Article in journal (Refereed) Published
Abstract [en]

Magneto-structural properties of films of diluted ferromagnetic alloys NixCu1-x in the concentration range 0.7 < x < 1.0 are studied experimentally. Films deposited by magnetron sputtering show partial phase separation, as evidenced by structural analysis and ferromagnetic resonance measurements. The phase diagram of the NixCu1-x bulk system is obtained using numerical theoretical analysis of the electronic structure, taking into account the interatomic exchange interactions. The results confirm the experimentally found partial phase separation, explain it as magnetic in origin, and indicate an additional metastable region connected with the ferromagnetic transition in the system.

Place, publisher, year, edition, pages
2012. Vol. 324, no 13, 2131-2135 p.
Keyword [en]
Dilute ferromagnet, Thin film, Phase diagram, Ferromagnetic resonance, Curie temperature
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-91299DOI: 10.1016/j.jmmm.2012.02.027ISI: 000301798900024Scopus ID: 2-s2.0-84858446128OAI: oai:DiVA.org:kth-91299DiVA: diva2:509294
Funder
EU, FP7, Seventh Framework Programme
Note
QC 20120423.  Updated from manuscript to article in journal.Available from: 2012-03-12 Created: 2012-03-12 Last updated: 2017-12-07Bibliographically 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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Korenivski, Vladislav

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