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Dynamics of skyrmionic states in confined helimagnetic nanostructures

Dynamics of skyrmionic states in confined helimagnetic nanostructures
Dynamics of skyrmionic states in confined helimagnetic nanostructures
In confined helimagnetic nanostructures, skyrmionic states in the form of incomplete and isolated skyrmion states can emerge as the ground state in absence of both external magnetic field and magnetocrystalline anisotropy. In this work, we study the dynamic properties (resonance frequencies and corresponding eigenmodes) of skyrmionic states in thin film FeGe disk samples. We employ two different methods in finite-element based micromagnetic simulation: eigenvalue and ringdown method. The eigenvalue method allows us to identify all resonance frequencies and corresponding eigenmodes that can exist in the simulated system. However, using a particular experimentally feasible excitation can excite only a limited set of eigenmodes. Because of that, we perform ringdown simulations that resemble the experimental setup using both in-plane and out-of-plane excitations. In addition, we report the nonlinear dependence of resonance frequencies on the external magnetic bias field and disk sample diameter and discuss the possible reversal mode of skyrmionic states. We compare the power spectral densities of incomplete skyrmion and isolated skyrmion states and observe several key differences that can contribute to the experimental identification of the state present in the sample. We measure the FeGe Gilbert damping, and using its value we determine what eigenmodes can be expected to be observed in experiments. Finally, we show that neglecting the demagnetisation energy contribution or ignoring the magnetisation variation in the out-of-film direction -- although not changing the eigenmode's magnetisation dynamics significantly -- changes their resonance frequencies substantially. Apart from contributing to the understanding of skyrmionic states physics, this systematic work can be used as a guide for the experimental identification of skyrmionic states in confined helimagnetic nanostructures.
1550-235X
1-16
Beg, Marijan
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Albert, Maximilian
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Bisotti, Marc-Antonio
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Cortes-Ortuno, David
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Wang, Weiwei
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Carey, Rebecca
fc5ef402-befe-4fff-ad14-c192eed54f36
Vousden, Mark
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Hovorka, Ondrej
a12bd550-ad45-4963-aa26-dd81dd1609ee
Ciccarelli, Chiara
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Spencer, Charles S.
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Marrows, Christopher H.
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Fangohr, Hans
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Beg, Marijan
5c7cc1ff-f244-471f-b964-9f24e0628153
Albert, Maximilian
a8049610-1e98-4cfb-b59a-177645a42b47
Bisotti, Marc-Antonio
be2d7abd-afdc-4d18-a2e9-a633d73a67b9
Cortes-Ortuno, David
97d026d6-1083-4edf-8ba6-2f66a3e15033
Wang, Weiwei
42981e5f-b7ee-44f7-a64d-d47ab0cacbce
Carey, Rebecca
fc5ef402-befe-4fff-ad14-c192eed54f36
Vousden, Mark
d45312dd-a46f-4376-89f4-38b1ac8957c9
Hovorka, Ondrej
a12bd550-ad45-4963-aa26-dd81dd1609ee
Ciccarelli, Chiara
defa490e-2f7c-4eb4-be82-bd453336544a
Spencer, Charles S.
d14ecfff-e370-4be4-8f87-41ea371d144f
Marrows, Christopher H.
412a62c5-225d-444b-8267-5340480591fd
Fangohr, Hans
9b7cfab9-d5dc-45dc-947c-2eba5c81a160

Beg, Marijan, Albert, Maximilian, Bisotti, Marc-Antonio, Cortes-Ortuno, David, Wang, Weiwei, Carey, Rebecca, Vousden, Mark, Hovorka, Ondrej, Ciccarelli, Chiara, Spencer, Charles S., Marrows, Christopher H. and Fangohr, Hans (2017) Dynamics of skyrmionic states in confined helimagnetic nanostructures. Physical Review B, 95 (1), 1-16, [014433]. (doi:10.1103/PhysRevB.95.014433).

Record type: Article

Abstract

In confined helimagnetic nanostructures, skyrmionic states in the form of incomplete and isolated skyrmion states can emerge as the ground state in absence of both external magnetic field and magnetocrystalline anisotropy. In this work, we study the dynamic properties (resonance frequencies and corresponding eigenmodes) of skyrmionic states in thin film FeGe disk samples. We employ two different methods in finite-element based micromagnetic simulation: eigenvalue and ringdown method. The eigenvalue method allows us to identify all resonance frequencies and corresponding eigenmodes that can exist in the simulated system. However, using a particular experimentally feasible excitation can excite only a limited set of eigenmodes. Because of that, we perform ringdown simulations that resemble the experimental setup using both in-plane and out-of-plane excitations. In addition, we report the nonlinear dependence of resonance frequencies on the external magnetic bias field and disk sample diameter and discuss the possible reversal mode of skyrmionic states. We compare the power spectral densities of incomplete skyrmion and isolated skyrmion states and observe several key differences that can contribute to the experimental identification of the state present in the sample. We measure the FeGe Gilbert damping, and using its value we determine what eigenmodes can be expected to be observed in experiments. Finally, we show that neglecting the demagnetisation energy contribution or ignoring the magnetisation variation in the out-of-film direction -- although not changing the eigenmode's magnetisation dynamics significantly -- changes their resonance frequencies substantially. Apart from contributing to the understanding of skyrmionic states physics, this systematic work can be used as a guide for the experimental identification of skyrmionic states in confined helimagnetic nanostructures.

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Accepted/In Press date: 5 December 2016
e-pub ahead of print date: 30 January 2017
Published date: January 2017
Organisations: Computational Engineering & Design Group

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Local EPrints ID: 403616
URI: http://eprints.soton.ac.uk/id/eprint/403616
ISSN: 1550-235X
PURE UUID: 3ec90b14-2d7d-4990-9191-2d5f0d981599
ORCID for Marijan Beg: ORCID iD orcid.org/0000-0002-6670-3994
ORCID for David Cortes-Ortuno: ORCID iD orcid.org/0000-0003-3799-3141
ORCID for Ondrej Hovorka: ORCID iD orcid.org/0000-0002-6707-4325
ORCID for Hans Fangohr: ORCID iD orcid.org/0000-0001-5494-7193

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Date deposited: 06 Dec 2016 17:03
Last modified: 08 Oct 2020 04:12

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Contributors

Author: Marijan Beg ORCID iD
Author: Maximilian Albert
Author: Marc-Antonio Bisotti
Author: David Cortes-Ortuno ORCID iD
Author: Weiwei Wang
Author: Rebecca Carey
Author: Mark Vousden
Author: Ondrej Hovorka ORCID iD
Author: Chiara Ciccarelli
Author: Charles S. Spencer
Author: Christopher H. Marrows
Author: Hans Fangohr ORCID iD

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