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Impact of the Oersted Field on Droplet Nucleation Boundaries
KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.ORCID-id: 0000-0001-9107-3309
Visa övriga samt affilieringar
2018 (Engelska)Ingår i: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, artikel-id 3104304Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

Ort, förlag, år, upplaga, sidor
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC , 2018. Vol. 9, artikel-id 3104304
Nyckelord [en]
Spin electronics, magnetic droplet, Oersted field, spin-torque nano-oscillators
Nationell ämneskategori
Strömningsmekanik och akustik
Identifikatorer
URN: urn:nbn:se:kth:diva-232425DOI: 10.1109/LMAG.2018.2850007ISI: 000438127100001Scopus ID: 2-s2.0-85049058526OAI: oai:DiVA.org:kth-232425DiVA, id: diva2:1235295
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF)VetenskapsrådetKnut och Alice Wallenbergs StiftelseEU, FP7, Sjunde ramprogrammet, 307144
Anmärkning

QC 20180725

Tillgänglig från: 2018-07-25 Skapad: 2018-07-25 Senast uppdaterad: 2018-09-11Bibliografiskt granskad
Ingår i avhandling
1. Engineering Magnetic Droplets in Nanocontact Spin-Torque Nano-Oscillators
Öppna denna publikation i ny flik eller fönster >>Engineering Magnetic Droplets in Nanocontact Spin-Torque Nano-Oscillators
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Spin-torque nano-oscillators (STNOs) are nanoscale spintronic devices capable of generating highly tunable broadband microwave signals. In this thesis, I study nanocontact (NC)-based STNOs using strong perpendicular magnetic anisotropy(PMA) free layers, where a novel magnetic soliton—a magnetic droplet—exists. This work is devoted to further understanding the characteristics of the magnetic droplet in diverse magnetic structures, including orthogonal and all-perpendicular(all-PMA) spin valves (SVs) and orthogonal magnetic tunnel junctions (MTJs). The nucleation, transition, and collapse of magnetic droplets are observed, tailored, and analyzed by engineering the magnetic properties of the thin films’ stacks. This thesis consists of three main parts: Orthogonal SVs with [Co/Ni]/Cu/CoxNiFe1−x: Magnetic droplets were first observed in orthogonal SV STNOs. We engineered the fixed layer magnetization Ms,p by cosputtering different compositions of CoxNiFe1−x (x = 0−1). The nucleation boundaries of a magnetic droplet in a current-field phase shift to a lower region as Ms,p decreases. The nucleation boundary is also examined under canted fields in order to better understand the drift instability of the droplets. The observations not only confirm the theoretical predictions of nucleation boundary, but suggest a method for controlling the nucleation boundary. All-PMA SVs with [Co/Ni]/Cu/[Co/Pd]: In contrast to orthogonal SVs,all-PMA NC-STNOs show many novel features. First, thanks to the dramatic improvement in droplet stability that results from using a [Co/Pd] PMA fixed layer, the droplets are directly imaged by a scanning transmission x-ray microscopy(STXM). The transition between the static bubble and magnetic droplet is also observed and imaged. Moreover, to investigate the effect of PMA, He+ irradiation is conducted on the all-PMA NC-STNOs, progressively tuning the PMA. The transitions of the normal FMR-like mode and droplet mode are demonstrated. The behavior of frequency tunability versus PMA is systematically studied. These investigations of all-PMA and irradiated NC-STNOs show that it is feasible to engineer the magnetic properties of STNOs through He+ irradiation. Besides, the dynamic droplets and static bubbles have great potential applications in next-generation information carriers. Orthogonal MTJs with CoFeB/MgO/CoFe: The existence of droplets in orthogonal MTJs is still debated. Instead, the magnetodynamics are investigated here. Very importantly, we find that the frequency tunability is determined by the spin-transfer torque (STT), the voltage-controlled magnetic anisotropy (VCMA), and thermal heating. This paves the way to improving tunability by combining these contributions. This study will contribute greatly to real applications, such as microwave generators and detectors.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2018. s. 74
Serie
TRITA-SCI-FOU ; 2018:36
Nyckelord
Magnetic Droplet, Magnetic Tunnel Junction, Perpendicular Magnetic Anisotropy, Spin-torque Nano-Oscillators, Spin-Valve.
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kth:diva-234464 (URN)978-91-7729-920-2 (ISBN)
Disputation
2018-10-04, Hall C, ​Electrum 229, Kista, 09:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF)VetenskapsrådetKnut och Alice Wallenbergs Stiftelse
Anmärkning

QC 20180907

Tillgänglig från: 2018-09-10 Skapad: 2018-09-06 Senast uppdaterad: 2018-09-18Bibliografiskt granskad

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