Change search
ReferencesLink to record
Permanent link

Direct link
Mutually synchronized bottom-up multi-nanocontact spin-torque oscillators
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
Show others and affiliations
2013 (English)In: Nature Communications, ISSN 2041-1723, Vol. 4, 2731- p.Article in journal (Refereed) Published
Abstract [en]

Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

Place, publisher, year, edition, pages
2013. Vol. 4, 2731- p.
Keyword [en]
Nano-Oscillators, Phase-Locking, Magnetic Multilayers, Polarized Current, Electric-Current, Modulation, Driven, Generation, Excitation, Waves
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-122705DOI: 10.1038/ncomms3731ISI: 000328023000002ScopusID: 2-s2.0-84889253383OAI: diva2:623402
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, European Research Council, ICT-257159

QC 20140114. Updated from submitted to published.

Available from: 2013-05-27 Created: 2013-05-27 Last updated: 2014-01-21Bibliographically approved
In thesis
1. Fabrication and Characterization of Nanocontact Spin-Torque Oscillators
Open this publication in new window or tab >>Fabrication and Characterization of Nanocontact Spin-Torque Oscillators
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The manufacturing of nanocontact-based spin-torque oscillators (NC-STOs)has opened the door for spintronic devices to play a part as active microwaveelements. The NC-STO has the capability of converting a direct current intoa microwave signal, and vice versa, by utilizing the spin transfer torque (STT)in ferromagnetic multilayer systems. However, the high-frequency operation ofNC-STOs typically requires high magnetic fields and the microwave power theygenerate is rather limited. As a result, NC-STOs are not yet commercially used,and they require improvements in both material systems and device geometriesbefore they can find actual use in microwave applications.

In order to improve and advance this technology, NC-STOs are requiredwith both different nanocontact (NC) sizes and geometries, and using differ- ent stacks of magnetic materials. This dissertation presents experimental in- vestigations into the manufacturing of such devices using different fabrication techniques and a number of different magnetic material stacks. Currently, the fabrication of NC-STOs is limited to advanced laboratories, because NC fabri- cation requires high-resolution lithography tools. In the present work, we have developed an alternative method of fabrication, which does not require such tools and has the capability of fabricating NC-STOs having one to hundreds of NCs in a variety of sizes, possibly  down to 20 nm. Devices fabricated with this method have shown mutual synchronization of three parallel-connected NCs, and pairwise synchronization in devices with four and five NCs.

Furthermore, the present work demonstrates low-field operation (down to0.02 Tesla) of NC-STOs at a record high frequency of 12 GHz. This wasachieved by implementing multilayers with a perpendicular magnetic anisotropy(PMA) material in the free layer of the NC-STO. In addition, the fabricateddevices revealed an unexpected dynamic regime under large external appliedfield (above 0.4 Tesla). The new dynamic regime was found to be due to anentirely novel nanomagnetic dynamic object â a so-called magnetic droplet soliton,predicted theoretically in 1977 but not experimentally observed until now.Detailed experiments and micromagnetic simulations show that the droplet hasvery rich dynamics.

Finally,  spin-torque-induced  transverse spin wave instabilities have beenstudied.  A NC-STO with  a material stack consisting of a single ferromag- netic metal sandwiched between two non-ferromagnetic metals was fabricated. Prior to this work, evidence of spin wave instabilities was reported as resis- tance switching in nanopillar- and mechanical point contact based STOs. In the present  work, the fabricated NC-STOs showed actual microwave  signals up to 3 GHz under zero applied field with strong current hysteresis. All  the fabricated NC-STOs open up new means of studying STT in different environ- ments, in order to resolve their current drawbacks for industrial applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xvi, 65 p.
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2013:04
Spin-torque oscillators, phase locking, spin wave, giant magnetoresistance, spin transfer torque, thin films.
National Category
Physical Sciences Nano Technology
urn:nbn:se:kth:diva-122292 (URN)978-91-7501-760-0 (ISBN)
Public defence
2013-06-14, Sal/Hall E, Foru KTH-ITC, Isafjordsgatan 39, Kista, 10:00 (English)

QC 20130527

Available from: 2013-05-27 Created: 2013-05-17 Last updated: 2014-01-14Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Redjai Sani, SohrabMohseni, Seyed MajidEklund, AndersMalm, GunnarÅkerman, Johan
By organisation
Material Physics, MFIntegrated Devices and Circuits
In the same journal
Nature Communications
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 315 hits
ReferencesLink to record
Permanent link

Direct link