References of "Ataklti, G. W"
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See detailFlux avalanches triggered by microwave depinning of magnetic vortices in Pb superconducting films
Awad, A. A.; Aliev, F. G.; Ataklti, G. W. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84(22), 224511

We observe abrupt changes in broadband microwave permeability of thin Pb superconducting films as functions of the microwave frequency and intensity, as well as of external magnetic field. These changes ... [more ▼]

We observe abrupt changes in broadband microwave permeability of thin Pb superconducting films as functions of the microwave frequency and intensity, as well as of external magnetic field. These changes are attributed to vortex avalanches generated by microwave induced depinning of vortices close to the sample edges. We map the experimental results on the widely used theoretical model assuming reversible response of the vortex motion to ac drive. It is shown that our measurements provide an efficient method of extracting the main parameter of the model—depinning frequencies—for different pinning centers. The observed dependences of the extracted depinning frequencies on the microwave power, magnetic field, and temperature support the idea that the flux avalanches are generated by microwave induced thermomagnetic instabilities. [less ▲]

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See detailCurrent-induced vortex trapping in asymmetric toothed channels
Cuppens, J.; Ataklti, G. W.; Moshchalkov, V. V. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84(18),

We investigate experimentally and theoretically the vortex dynamics in a superconducting film with nanoengineered open vortex traps which provide tunable pinning, ranging from no pinning for a certain ... [more ▼]

We investigate experimentally and theoretically the vortex dynamics in a superconducting film with nanoengineered open vortex traps which provide tunable pinning, ranging from no pinning for a certain current direction to finite pinning when reversing the current flow. The design is based on the confinement of the vortex motion within two repulsive walls, one with periodic microprotrusions and the other one smooth. Clear commensurability effects are seen if the bias current drives the vortices inside the traps, whereas these effects are much less pronounced when the current pushes the vortices against the smooth surface. For small periods of the protrusions or large vortex sizes, the properties displayed by the vortices, pushed against these two surfaces of dissimilar roughness can be thought of as due to the change of effective sliding friction. [less ▲]

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See detailMesoscopic cross-film cryotrons: Vortex trapping and dc-Josephson-like oscillations of the critical current
Aladyshkin, A Yu; Ataklti, G. W.; Gillijns, W. et al

in Physical Review. B : Condensed Matter (2011), 83(14),

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the ... [more ▼]

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the superconducting strip. It is well known that the critical current of the superconducting strip, I(c), in such a cryotron-like system can be tuned by changing the current in the control wire, I(w). We demonstrated that the discrete change in the number of the pinned vortices/antivortices inside the narrow and long strip nearby the current-carrying wire results in a peculiar oscillatory dependence of I(c) on I(w). [less ▲]

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See detailVisualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging
Motta, M.; Colauto, F.; Zadorosny, R. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84(21), 214529

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical ... [more ▼]

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements. [less ▲]

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See detailLocal probing of the vortex-antivortex dynamics in superconductor/ferromagnet hybrid structures
Silhanek, Alejandro ULg; Gladilin, V. N.; Van de Vondel, J. et al

in Superconductor Science and Technology (2011), 24(2),

In-plane ferromagnetic bars, densely packed in a linear array underneath a superconducting bridge, create two types of vortex chains of opposite polarity inside the superconductor. In this work we ... [more ▼]

In-plane ferromagnetic bars, densely packed in a linear array underneath a superconducting bridge, create two types of vortex chains of opposite polarity inside the superconductor. In this work we investigate both experimentally and theoretically the dynamics of these vortex chains as a function of an external magnetic field for two different arrangements of magnetic moments, namely parallel and antiparallel. The theoretical approach, based on the time-dependent Ginzburg-Landau formalism, confirms previously proposed empirical models implemented to describe the basic properties of these hybrid systems. In addition, local transport measurements allow us to probe the dynamics of individual vortex channels as a function of the applied magnetic field. These measurements evidence a drastic reduction of the dissipation in the channel populated with vortices having opposite polarity to the applied field. [less ▲]

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See detailMicroscopic picture of the critical state in a superconductor with a periodic array of antidots
Silhanek, Alejandro ULg; Gutierrez, J.; Kramer, R. B. G. et al

in Physical Review. B : Condensed Matter (2011), 83(2),

By using scanning Hall microscopy we visualize the progressive formation of the critical state with individual vortex resolution in a Pb thin film with a periodic pinning array. Slightly above the first ... [more ▼]

By using scanning Hall microscopy we visualize the progressive formation of the critical state with individual vortex resolution in a Pb thin film with a periodic pinning array. Slightly above the first penetration field, we directly observe a terraced critical state as proposed theoretically by Cooley and Grishin [Phys. Rev. Lett. 74, 2788 (1995)]. However, at higher fields, the flux front tends to disorder and the classical Bean profile is restored. This study allows us to establish a clear link between the widely used integrated response measurements in the superconducting state and the nanoscale landscape defined by individual vortices. [less ▲]

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See detailVortex Dynamics in a Superconducting Film with a Kagome and a Honeycomb Pinning Landscape
Cuppens, J.; Ataklti, G. W.; Gillijns, W. et al

in Journal of Superconductivity & Novel Magnetism (2011), 24(1-2), 7-11

The vortex dynamics in a superconducting thin Al film with a periodic Honeycomb or Kagome array of antidots has been investigated by electrical transport measurements. The large values of the ... [more ▼]

The vortex dynamics in a superconducting thin Al film with a periodic Honeycomb or Kagome array of antidots has been investigated by electrical transport measurements. The large values of the superconducting coherence length and penetration depth of the Al films guarantee a maximum of one flux quantum trapped per pinning site. This allows us to directly compare the experimental results with previous theoretical investigations based on molecular dynamics simulations. For the Kagome lattice, two submatching features not anticipated theoretically at H/H (1)=1/3 and 2/3, where H (1) is the field at which the number of vortices coincides with the number of pinning sites, are observed. Possible corresponding stable vortex patterns are suggested. For the Honeycomb pinning landscape, the commensurability effects are in agreement with the theoretical expectations. A preliminary analysis of the vortex mobility in this lattice shows the presence of a weak vortex guidance. [less ▲]

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See detailField polarity dependent nucleation of superconductivity in quasi-one-dimensional magnetic templates
Ataklti, G. W.; Silhanek, Alejandro ULg; Van de Vondel, J. et al

in Physica C: Superconductivity (2010), 470(19), 860-862

We investigate the nucleation of superconductivity in an Al/Al(2)O(3)/Py trilayer system by electrical transport measurements. Magnetic force microscopy images taken at room temperature show that the 0.7 ... [more ▼]

We investigate the nucleation of superconductivity in an Al/Al(2)O(3)/Py trilayer system by electrical transport measurements. Magnetic force microscopy images taken at room temperature show that the 0.7 mu m thick Py-film form stripes of magnetic domains with alternating out-of-plane stray field. After applying a strong out of plane magnetic field H the superconductor/normal phase boundary becomes asymmetric with respect to H = 0. This lack of field polarity symmetry results from the unbalanced size distribution of domains with opposite polarity. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailDirect visualization of the Campbell regime in superconducting stripes
Kramer, R. B. G.; Ataklti, G. W.; Moshchalkov, V. V. et al

in Physical Review. B : Condensed Matter (2010), 81(14),

A combination of scanning Hall microscopy and scanning ac-susceptibility measurements in superconducting stripes (ribbons) of width w < 10 mu m was used to observe the dimensional phase transitions of the ... [more ▼]

A combination of scanning Hall microscopy and scanning ac-susceptibility measurements in superconducting stripes (ribbons) of width w < 10 mu m was used to observe the dimensional phase transitions of the vortex lattice and its stability under alternating fields. At low dc magnetic fields applied perpendicularly to the plane of the stripes, vortices form a one-dimensional chain at the center of the stripes. Above a certain field H*(w), the vortex chain splits in two parallel rows displaced laterally in such a way that a zigzag vortex pattern is observed. By shaking the vortices with an external magnetic ac field and detecting their in-phase motion locally, we can identify the degree of mobility of each individual vortex. This technique allows us (i) to directly visualize the transition from intravalley (Campbell regime) to intervalley vortex motion as the amplitude of the ac modulation is increased and (ii) to accurately determine the temperature at which the vortex lattice freezes in a field-cooling experiment. [less ▲]

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See detailField polarity dependent superconducting properties in a superconductor/ferromagnet hybrid with in-plane magnetic moment
Gillijns, W.; Godts, F.; Ataklti, G. W. et al

in Physica C: Superconductivity (2010), 470(19), 880-882

The transport properties of an Al type-II superconducting thin film covering a Py plain film with a rectangular array of triangular holes are investigated. We show that, although the magnetization of the ... [more ▼]

The transport properties of an Al type-II superconducting thin film covering a Py plain film with a rectangular array of triangular holes are investigated. We show that, although the magnetization of the Py lies in the plane of the structure, both the critical temperature and the critical current are asymmetric with respect to the polarity of the external field, which is applied perpendicularly to the structure. The asymmetric nucleation can be explained in terms of field compensation effects between internal and external magnetic fields, whereas the presence of vortex-antivortex pairs are responsible for the observed features in the critical current. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailPinning centers produced by magnetic microstructures
Silhanek, Alejandro ULg; Van de Vondel, J.; Leo, A. et al

in Superconductor Science and Technology (2009), 22(3),

We investigate the flux pinning and dynamic properties of superconducting vortices in an Al film with an array of magnetic bars deposited on top. The dimensions of each bar are chosen in such a way that ... [more ▼]

We investigate the flux pinning and dynamic properties of superconducting vortices in an Al film with an array of magnetic bars deposited on top. The dimensions of each bar are chosen in such a way that they host a single magnetic domain. These micromagnets are distributed periodically in a rectangular array with 0.5 mu m separation parallel to the longest side of the bars and displaced laterally by a distance w. We show that, for w > Lambda, where Lambda is the effective field penetration depth, the pinning strength is almost independent of w whereas the critical temperature at zero field, T(c)(0), decreases as similar to w(-1). For w < Lambda the opposite behavior is observed, i.e. T(c)(0) seems to saturate to a nearly w-independent value and the transition from large to small w is accompanied by a large suppression of the critical current j(c) together with a clear change in the shape of the current-voltage characteristics. In particular, the substantial weakening of the pinning potential for w < Lambda gives rise to an unexpected flux flow response. The field evolution of this regime allows us to determine whether the magnetic bars induce vortex-antivortex pairs in the system. The present findings suggest that practical application of magnetic pinning centers are restricted to low field values. [less ▲]

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