Skyrmion based microwave detectors and harvesting

We theoretically reveal that pure eigenmodes of an isolated magnetic skyrmion embedded in a ferromagnetic environment can be selectively activated using microwave electric fields without exciting gigantic ferromagnetic resonances, in contrast to conventional methods using microwave magnetic fields. We also demonstrate that this selective activation of a skyrmion can efficiently drive its translational motion in a ferromagnetic nanotrack under application of an external magnetic field inclined from the normal direction. We find that a mode with combined breathing and rotational oscillations induces much faster skyrmion propagation than the breathing mode studied previously by Wang et al. [Phys. Rev. B 92, 020403(R) (2015)].A skyrmion crystal, a hexagonally crystalized state of magnetic skyrmions 1-6 , has characteristic resonance modes at microwave frequencies 7-10 , which give rise to intriguing physical phenomena 11 such as microwave directional dichroism 12-15 , spin-voltage induction 16,17 , and spin-current generation 18 . When a static magnetic field H ex is applied perpendicular to a thin-plate specimen of the skyrmion-hosting magnet, several types of spinwave modes emerge depending on the microwave polarization 7 . A microwave magnetic field H ω normal to24 sites 24 sites T=0 T=30 T=0 T=30 FIG. 1. (color online). (a) Schematics of a magnetic bilayer system hosting skyrmions stabilized by the interfacial Dzyaloshinskii-Moriya interaction. (b) External magnetic field Hex where θ is an inclination angle from the normal direction. (c), (d) Color maps of the normal component of magnetizations mz (c) and scalar spin chiralities cs (d) of a skyrmion under a perpendicular Hex field. In-plane components of the magnetizations (mx, my) are displayed by arrows. (e), (f) Those under an inclined Hex field with θ=30 • .the skyrmion plane (H ω ⊥ ) activates the so-called breathing mode in which all the skyrmions constituting the skyrmion crystal uniformly expand and shrink in an oscillatory manner. On the other hand, the H ω field within the skyrmion plane (H ω ) activates two types of rotation modes with opposite rotational senses, in which cores of all the skyrmions circulate uniformly in counterclockwise and clockwise ways.In addition to the crystallized form, skyrmions can appear as individual defects in a ferromagnetic state; such skyrmions are also expected to have peculiar collective modes 19 . Isolated skyrmions confined in a nanoferromagnet are potentially useful for applications 20 to memory devices 21 , magnonics devices 22-24 , spin-torque oscillators 25,26 , and microwave sensing devices 27 . As such, it is necessary to clarify the microwave-active eigenmodes of a single skyrmion in a ferromagnetic specimen.In addition, it is important to establish a way to manipulate isolated skyrmions using microwaves for their device application. As the microwave field H ω ⊥ cannot activate precessions of the magnetizations when the microwave field is applied parallel to them, we can activate pure breathing-type skyrmion o...

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“…We take J=1 for the energy units and take D 0 /J=0. 27. For the inclined magnetic field, we take H z =0.057 with θ being a variable.…”

Section: (C) and (D)]mentioning

confidence: 99%

Selective activation of an isolated magnetic skyrmion in a ferromagnet with microwave electric fields

Takeuchi

Mochizuki

2018

Applied Physics Letters

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“…Similarly to optics2122, the excitation of spiral spin-waves in magnetism could be attractive for designing new information coding protocols. Recent experimental observations have demonstrated that skyrmions1516232425 can be nucleated via conversion of domain walls in Ta/CoFeB/MgO26, or by applying an out-of-plane field in Ir/Co/Pt27 and Pt/Co/MgO28 multilayers. Although a single skyrmion can be nucleated by a spin-polarized scanning tunneling microscope29, the control of its room temperature nucleation is still an experimental challenge.…”

mentioning

confidence: 99%

Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves

Giordano

Verba

Zivieri

et al. 2016

Sci Rep

Self Cite

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Spin-Hall oscillators (SHO) are promising sources of spin-wave signals for magnonics applications, and can serve as building blocks for magnonic logic in ultralow power computation devices. Thin magnetic layers used as “free” layers in SHO are in contact with heavy metals having large spin-orbital interaction, and, therefore, could be subject to the spin-Hall effect (SHE) and the interfacial Dzyaloshinskii-Moriya interaction (i-DMI), which may lead to the nonreciprocity of the excited spin waves and other unusual effects. Here, we analytically and micromagnetically study magnetization dynamics excited in an SHO with oblique magnetization when the SHE and i-DMI act simultaneously. Our key results are: (i) excitation of nonreciprocal spin-waves propagating perpendicularly to the in-plane projection of the static magnetization; (ii) skyrmions generation by pure spin-current; (iii) excitation of a new spin-wave mode with a spiral spatial profile originating from a gyrotropic rotation of a dynamical skyrmion. These results demonstrate that SHOs can be used as generators of magnetic skyrmions and different types of propagating spin-waves for magnetic data storage and signal processing applications.

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“…Skyrmion-based devices have also been designed to make logic gates in which the duplication or merging of skyrmions is used to perform logic operations [117]. We could also cite the exploitation of the interaction of magnons with skyrmions for the design of skyrmion magnonic crystals for tunable rf filtering [118] or the development of rf oscillators based on the specific dynamical modes of skyrmionic spin configurations [119].…”

Section: Hdmi = (S1  S2)d12 (Eq2)mentioning

confidence: 99%

Spintronics, from giant magnetoresistance to magnetic skyrmions and topological insulators

Fert

Dau

2019

Comptes Rendus. Physique

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This article aims at giving a general presentation of spintronics, an important field of research developing today along many new directions in physics of condensed matter. We tried to present simply the physical phenomena involved in spintronicsno equations but many schematics. We also described the applications of spintronics, those of today and those expected to have an important impact on the next developments of the information and communication technologies. This article was published in the Comptes Rendus Physique of the French Academy of Sciences (https://doi.

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Skyrmion based microwave detectors and harvesting

Cited by 100 publications

References 42 publications

Selective activation of an isolated magnetic skyrmion in a ferromagnet with microwave electric fields

Selective activation of an isolated magnetic skyrmion in a ferromagnet with microwave electric fields

Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves

Spintronics, from giant magnetoresistance to magnetic skyrmions and topological insulators

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