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Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator
Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
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2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 19, article id 192405Article in journal (Refereed) Published
Abstract [en]

Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nanooscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a nonlinear "bullet" mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is increased above threshold, the bullet mode appears to increase in size, suggesting increased translational motion. The reduced spatial overlap of the bullet and FMR modes, and this putative translational motion, may impede the injection locking and contribute to the reduced locking range observed within NC-SHNO devices. This illustrates a more general need to control the geometry of an injection-locked oscillator so that the autonomous dynamics of the oscillator exhibit strong spatial overlap with those resulting from the injected signal..

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018. Vol. 113, no 19, article id 192405
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Physical Sciences
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URN: urn:nbn:se:kth:diva-239481DOI: 10.1063/1.5047148ISI: 000449713800021Scopus ID: 2-s2.0-85056496103OAI: oai:DiVA.org:kth-239481DiVA, id: diva2:1265655
Note

QC 20181126

Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2018-11-26Bibliographically approved

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