Tunable ratchet effects for vortices pinned by periodic magnetic dipole arrays

Carneiro, Gilson

doi:10.1016/j.physc.2005.08.005

Cited by 21 publications

(20 citation statements)

References 16 publications

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“…22,23 This ratchet is based on pinning by arrays of magnetic dipoles, and this model has been applied in the case of superconducting vortices. In this theory, the origin of this pure magnetic ratchet effect is the periodic vortex pinning potential with broken reflection symmetry created by the magnetic dipoles.…”

Section: Resultsmentioning

confidence: 99%

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Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Lara

Castaño

et al. 2009

Phys. Rev. B

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A ratchet effect ͑the rectification of an ac injected current͒ which is purely magnetic in origin has been observed in a superconducting-magnetic nanostructure hybrid. The hybrid consists of a superconducting Nb film in contact with an array of nanoscale magnetic triangles, circular rings, or elliptical rings. The arrays were placed into well-defined remanent magnetic states by application of different magnetic field cycles. The stray fields from these remanent states provide a magnetic landscape which influences the motion of superconducting vortices. We examined both randomly varying landscapes from demagnetized samples and ordered landscapes from samples at remanence after saturation in which the magnetic rings form parallel onion states containing two domain walls. The ratchet effect is absent if the rings are in the demagnetized state or if the vortices propagate parallel to the magnetic reflection symmetry axis ͑perpendicular to the magnetic domain walls͒ in the ordered onion state. On the other hand, when the vortices move perpendicular to the magnetic reflection symmetry axis in the ordered onion state ͑parallel to the domain walls͒ a clear ratchet effect is observed. This behavior differs qualitatively from that observed in samples containing arrays of triangular Ni nanostructures, which show a ratchet of structural origin.

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Section: Resultsmentioning

confidence: 99%

“…These results were analyzed with the aforementioned model 21,22 invoking the appearance of vortex-antivortex pairs. However, contrary to our results, several polarity reversals were observed with increasing number of vortices.…”

Section: Resultsmentioning

confidence: 99%

Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Lara

Castaño

et al. 2009

Phys. Rev. B

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“…V where rows of vortices and antivortices generated by the magnetic template coexist, makes our system similar to the array of elongated magnetic bars studied by de Souza Silva et al 9 This system has been modeled within the London approximation by Carneiro 8 for the case where no v-av pairs are induced, and more recently by Lima and de Souza Silva 23 assuming that v-av pairs emanate from the dipoles. Irrespective of whether the magnetic template is able to induce v-av pairs or not, both situations lead to a rectification of the net vortex motion v when a zero average ac force is applied parallel to the dipolar moment ͑i.e., along the line connecting a vortex with its corresponding antivortex͒.…”

Section: Determination Of the V-av Pairs Density At Low Frequencimentioning

confidence: 90%

“…Indeed, the fact that the critical force to bring the vortex and antivortex closer differs from that necessary to pull them apart, 8 gives rise to a clear rectification effect when the system is submitted to a zero average ac signal. This rectified voltage is maximum at zero external field 9 and progressively decreases with increasing field until all vortices ͑or antivortices͒ are compensated.…”

Section: U P ͑R͒mentioning

confidence: 99%

Self-organized mode-locking effect in superconductor/ferromagnet hybrids

et al. 2009

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The vortex dynamics in a low-temperature superconductor deposited on top of a rectangular array of micrometer size permalloy triangles is investigated experimentally. The rectangular unit cell is such that neighboring triangles physically touch each other along one direction. This design stabilizes remanent states which differ from the magnetic vortex state typical of individual noninteracting triangles. Magnetic force microscopy images have revealed that the magnetic landscape of the template can be switched to an ordered configuration after magnetizing the sample with an in-plane field. The ordered phase exhibits a broad flux-flow regime with relatively low critical current and a highly anisotropic response. This behavior is caused by the spontaneous formation of two separated rows of vortices and antivortices along each line of connected triangles. The existence of a clear flux-flow regime at zero external field supports this interpretation. The density of induced vortex-antivortex pairs is directly obtained using a high-frequency measurement technique which allows us to resolve the discrete motion of vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a self-organized synchronized motion of vortices which manifests itself as field independent Shapiro steps in the current-voltage characteristics.

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“…As recently proposed by Carneiro [9], a different way to create vortex ratchets can be realized by using in-plane magnetized dots. Here the spatial inversion symmetry is broken not by the shape of the pinning sites but rather by the vortex-magnetic-dipole interaction.…”

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confidence: 99%

Dipole-Induced Vortex Ratchets in Superconducting Films with Arrays of Micromagnets

et al. 2007

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We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by magnetic force microscopy imaging, the magnetic state of both systems can be adjusted to produce arrays of almost pointlike magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role in the transport properties of this hybrid system. DOI: 10.1103/PhysRevLett.98.117005 PACS numbers: 74.78.Na, 05.40.ÿa, 74.25.Fy, 85.25.ÿj Nanoengineered arrays of vortex pinning sites have recently spawned numerous novel phenomena and potential applications based on vortex manipulation in superconductors. These structures are very suitable for tailoring the critical current and equilibrium properties [1-3] as well as for manipulating the distribution and direction of motion of flux quanta in superconducting devices [4 -7]. Such a control of vortex motion can be achieved when the periodic pinning potential lacks the inversion symmetry in a given direction, in which case any correlated fluctuating force induces a net vortex motion based on the phenomenon known as ratchet effect [8].As recently proposed by Carneiro [9], a different way to create vortex ratchets can be realized by using in-plane magnetized dots. Here the spatial inversion symmetry is broken not by the shape of the pinning sites but rather by the vortex-magnetic-dipole interaction. This dipoleinduced ratchet motion depends on the orientation and strength of the local magnetic moments thus allowing one to control the direction of the vortex drift. It is particularly this flexibility to manipulate the vortex motion which makes this kind of pinning potentials attractive for practical applications, although still a clear experimental corroboration is pending. In the present work, we demonstrate in a series of transport experiments that in-plane magnetized dipoles can indeed rectify vortex motion. Moreover, the rectified voltage induced by the ratchet motion depends strongly on temperature and field intensity and is nonzero even at zero field. Our analysis suggests that this behavior results from the interaction between the external field-induced vortices and vortex-antivortex pairs generated by magnetic dipoles.Our measurements were performed on two samples with different magnetic templates: (i) a 50 nm thick Al film with an on-top square array (period a p 3 m) of Si=Co=Au bars (with thicknesses 5 nm=47 nm=5 nm and lateral dimensions 2:6 0:5 m 2 ), labeled Bar-Al, and (ii) a Ge=Pb=Ge trilayer (20 nm=25 nm=5 nm thick) evaporated on top of a close-packed square array of equilateral triangular Co rings (250 nm wide, 23 nm thick, with lateral siz...

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Tunable ratchet effects for vortices pinned by periodic magnetic dipole arrays

Cited by 21 publications

References 16 publications

Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Self-organized mode-locking effect in superconductor/ferromagnet hybrids

Dipole-Induced Vortex Ratchets in Superconducting Films with Arrays of Micromagnets

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