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KTH

1. Persson, Milton. Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs.

Degree: Nanostructure Physics, 2019, KTH

Spin-vortices in vertically spaced pairs of thin elliptical Permalloy nanoparticles are investigated. The two vortex cores with parallel out-of-plane magnetization exhibit a strong monopole-like attraction through the spacer much thinner than the core length, thus forming a bound core-core pair. The material of the spacer is designed to suppress both direct and indirect exchange interactions, so the remaining inter-vortex coupling is purely dipolar. In the investigated vortex pairs, the in-plane magnetization in the vortex periphery, outside the vortex cores, curl in opposite directions (have opposite chirality). As a result, the two cores move in opposite directions in response to an in-plane magnetic field, the Zeeman effect of which acts to decouple the core-core pair. This leads to unique dynamics of the spin-vortex parallel-core/antiparallel-chirality pair, which strongly depend on whether the pair is coupled or decoupled. In the coupled state, the cores are held close together by the core-core attraction, which results in short-radius oscillations and a resonance frequency of about 2 GHz for the main rotational eigen-mode. In the decoupled state, the cores are separated by a distance much greater than the core length and gyrate independently with a resonance frequency of the order of 100 MHz. The dynamics of the vortex pair are investigated at 77 K, where there is a bistability between the coupled and decoupled core states. Resonant excitations are used to decouple the cores with pulses of ∼10 Oe in amplitude and ∼100 ps in duration. The ability to decouple a vortex pair using such fast low-power pulses can be useful for multifrequency oscillators and vortex based memory. A search for quantum effects is undertaken at sub-Kelvin temperatures using a dilution refrigerator. Square pulses of 100 ns duration and amplitudes of the order of 1 Oe are applied in-plane to bring the system closer to decoupling, giving the cores a chance to tunnel through the barrier between the coupled and decoupled states. The amplitude required for decoupling is measured as a function of temperature and a leveling off in the decoupling probability is seen below 400 mK, giving some indication of core tunneling. Macroscopic quantum tunneling of magnetization is interesting from the fundamental physics point of view, e.g., as a model system for studying the measurement paradox in quantum mechanics, as well as for current and future computer technology in terms of understanding the ultimate limitations of miniaturizing magnetic memory elements.

I detta arbete studeras spinnvirvlar i elliptiska skivor av Permalloy ordnade i vertikala par. Kärnor av parallell vertikal magnetisering attraherar varandra likt monopoler genom en film mycket tunnare än kärnorna och bildar därmed ett sammankopplat par. Materialet i filmen mellan virvlarna är designat för att förhindra både direkt och indirekt utbytesväxelverkan och lämnar endast kärnornas dipolväxelverkan. I de virvelpar som studeras går den plana magnetiseringen i…

Subjects/Keywords: Spin-vortex; ultra fast vortex dynamics; milli-Kelvin temperatures; macroscopic quantum tunneling; Spinnvirvel; ultrasnabb virveldynamik; milli-Kelvin temperaturer; makroskopisk kvanttunnling; Condensed Matter Physics; Den kondenserade materiens fysik

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Persson, M. (2019). Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs. (Thesis). KTH. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-242225

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Persson, Milton. “Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs.” 2019. Thesis, KTH. Accessed February 22, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-242225.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Persson, Milton. “Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs.” 2019. Web. 22 Feb 2019.

Vancouver:

Persson M. Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs. [Internet] [Thesis]. KTH; 2019. [cited 2019 Feb 22]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-242225.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Persson M. Transient Dynamics and Core Tunneling in Vertical Spin-Vortex Pairs. [Thesis]. KTH; 2019. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-242225

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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