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Low operational current spin Hall nano-oscillators based on NiFe/W bilayers
KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.ORCID-id: 0000-0003-3605-8872
KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
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2016 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, nr 24, artikel-id 242402Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/beta-W bilayers. Thanks to the very high spin Hall angle of beta-W, we achieve more than a 60% reduction in the auto-oscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from beta-W. Published by AIP Publishing.

Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP), 2016. Vol. 109, nr 24, artikel-id 242402
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-201252DOI: 10.1063/1.4971828ISI: 000391457500025Scopus ID: 2-s2.0-85006791339OAI: oai:DiVA.org:kth-201252DiVA, id: diva2:1074400
Anmärkning

QC 20170215

Tillgänglig från: 2017-02-15 Skapad: 2017-02-15 Senast uppdaterad: 2018-09-07Bibliografiskt granskad
Ingår i avhandling
1. Linear, Non-Linear, and Synchronizing Spin Wave Modes in Spin Hall Nano-Oscillators
Öppna denna publikation i ny flik eller fönster >>Linear, Non-Linear, and Synchronizing Spin Wave Modes in Spin Hall Nano-Oscillators
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Spin Hall nano-oscillators (SHNOs) are nanoscale spintronic devices that generate microwave signals with highly tunable frequency. This thesis focuses on improving the signal quality of nanoconstriction-based SHNOs and also on developing a better understanding of their magnetization dynamics.

In the first part of the thesis, we fabricate and characterize low-threshold current SHNOs using NiFe/β-W bilayers. Due to the high spin Hall angle of the β-phase W, the auto-oscillation threshold current is improved by 60% over SHNOs based on NiFe/Pt. We also demonstrate low operational current by utilizing W/Co20Fe60B20/MgO stacks on highly resistive silicon substrates. Thanks to the moderate perpendicular magnetic anisotropy (PMA) of Co20Fe60B20, these SHNOs show much wider frequency tunability than SHNOs based on NiFe with no PMA. Performance is further improved by using highly resistive silicon substrates with a high heat conductance, dissipating the generated excess heat much better than sapphire substrates. Moreover, it also means that the fabrication of SHNOs is now compatible with conventional CMOS fabrication, which is necessary if SHNOs are to be used in integrated circuits. In another approach, we attempt to decrease the threshold current of SHNOs based on an NiFe/Pt stack by inserting an ultra-thin Hf layer in the middle of the stack. This Hf dusting decreases the damping of the bilayer linearly but also degrades its spin Hall efficiency. These opposing trends determine the optimum Hf thickness to ≈0.4 nm, at which the auto-oscillation threshold current is minimum. Our achievements arising from these three approaches show a promising path towards the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque.

In the next chapter, we use both electrical experimentation and micromagnetic simulation to study the auto-oscillating spin wave modes in nanoconstriction-based SHNOs as a function of the drive current and the applied field. First, we investigate the modes under an in-plane low-range field of 40-80 mT, which is useful for developing low-field spintronic devices with applications in microwave signal generation. It is also essential for future studies on the synchronization of multiple SHNOs. Next, using an out-of-plane applied magnetic field, we observe three different modes and demonstrate switching between them under a fixed external field by tuning only the drive current. The flexibility of these nanopatterned spin Hall nano-oscillators is desirable for implementing oscillator-based neuromorphic computing devices.

In the final part, we study the synchronization of multiple nanoconstriction-based SHNOs in weak in-plane fields. We electrically investigate the synchronization versus the angle of the field, observing synchronization for angles below a threshold angle. In agreement with the experimental results, the spatial profile of the spin waves from the simulations shows that the relative angle between the modes from the nanoconstrictions decreases with decreasing the field angle, thus facilitating synchronization. The synchronization observed at low in-plane fields improves the microwave signal quality and could also be useful for applications such as neuromorphic computing.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2018. s. 58
Serie
TRITA-SCI-FOU ; 2018:37
Nyckelord
spin Hall effect, spin Hall nano-oscillators, threshold current, microwave, spin wave, synchronization
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kth:diva-234657 (URN)978-91-7729-929-5 (ISBN)
Disputation
2018-10-05, Sal Sven-Olof Öhrvik, Kistagången 16, Electrum 1, floor 2, KTH Kista, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20180907

Tillgänglig från: 2018-09-07 Skapad: 2018-09-07 Senast uppdaterad: 2018-09-10Bibliografiskt granskad

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