References of "Moshchalkov, V. V."
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See detailComment on "Transverse rectification in superconducting thin films with arrays of asymmetric defects" [Appl. Phys. Lett. 91, 062505 (2007)]
Silhanek, Alejandro ULg; de Vondel, J Van; Moshchalkov, V. V. et al

in Applied Physics Letters (2008), 92(17),

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See detailRectification effects in superconductors with magnetic pinning centers
Silhanek, Alejandro ULg; Verellen, N.; Metlushko, V. et al

in Physica C: Superconductivity (2008), 468(7-10), 563-567

We investigate the dynamics and pinning properties of vortices in superconducting At films deposited on top of a close-packed array of Py microsized. loops by electrical transport measurements. The ... [more ▼]

We investigate the dynamics and pinning properties of vortices in superconducting At films deposited on top of a close-packed array of Py microsized. loops by electrical transport measurements. The micromagnets have an in-plane magnetic moment that can be set in different magnetic states by applying an external field parallel to the plane of the pattern. When the loops are set in the magnetic vortex-state, for which the stray field is the smallest, a weaker pinning in comparison with the polarized states (i.e. strong stray field) is observed. In addition, a clear influence of the chosen magnetic state of the Py rings on the dynamics of the vortex motion under an ac-excitations is obtained. When the magnetic elements are in the as-grown state a rectification signal which reverses sign when the field changes polarity is observed. In contrast to that, when the array of loops is magnetized the observed rectification effect is independent of the field polarity and can be reversed by reorienting the magnetization of the micromagnets. (c) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailVoltage rectification effects in mesoscopic superconducting triangles: Experiment and modeling
Schildermans, N.; Kolton, A. B.; Salenbien, R. et al

in Physical Review. B : Condensed Matter (2007), 76(22),

The interaction of externally applied currents with persistent currents induced by magnetic field in a mesoscopic triangle is investigated. As a consequence of the superposition of these currents, clear ... [more ▼]

The interaction of externally applied currents with persistent currents induced by magnetic field in a mesoscopic triangle is investigated. As a consequence of the superposition of these currents, clear voltage rectification effects are observed. We demonstrate that the amplitude of the rectified signal strongly depends on the configurations of the current leads with the lowest signal obtained when the contacts are aligned along a median of the triangle. When the contacts are aligned off centered compared to the geometrical center, the voltage response shows oscillations as a function of the applied field, whose sign can be controlled by shifting the contacts. These results are in full agreement with theoretical predictions for an analogous system consisting of a closed loop with a finite number of identical Josephson junctions. [less ▲]

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See detailDipole-induced vortex ratchets in superconducting films with arrays of micromagnets
de Souza Silva, C. C.; Silhanek, Alejandro ULg; Van de Vondel, J. et al

in Physical Review Letters (2007), 98(11),

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 ... [more ▼]

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. [less ▲]

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See detailInfluence of magnet size on magnetically engineered field-induced superconductivity
Gillijns, W.; Milosevic, M. V.; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2007), 76(18),

We investigate experimentally and theoretically the superconducting properties of an Al thin film covering a periodic array of Co/Pt magnetic disks with out-of-plane magnetization for different radii of ... [more ▼]

We investigate experimentally and theoretically the superconducting properties of an Al thin film covering a periodic array of Co/Pt magnetic disks with out-of-plane magnetization for different radii of the magnetic disks and constant period of the magnetic lattice. The presence of the arrays of magnetic dots leads to a quantized displacement of the normal/superconducting phase boundary along the magnetic field axis, with each step corresponding to a flux-quantum per unit cell of the magnetic lattice. We demonstrate that this so-called field-induced superconductivity is strongly dependent not only on the chosen magnetic material and its magnetization M but also on the radius R of the constructed magnetic disks. Since field-induced superconductivity is directly linked to the nucleation of vortex-antivortex (V-AV) pairs, a theoretical M-R equilibrium phase boundary is presented, delimiting regions of different numbers of induced V-AV pairs per magnet. A good qualitative and quantitative agreement is found between theory and experiment. [less ▲]

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See detailOrigin of reversed vortex ratchet motion
Gillijns, W.; Silhanek, Alejandro ULg; Moshchalkov, V. V. et al

in Physical Review Letters (2007), 99(24),

We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also ... [more ▼]

We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also essentially depends on the ratio between the characteristic interaction distance and the period of the asymmetric pinning potential. We study four samples with different periods d of the asymmetric potential. For large d the dc voltage V(dc) recorded under a ac excitation indicates that the average vortex drift is from bigger to smaller dots for all explored positive fields. As d is reduced, a series of sign reversals in the dc response are observed as a function of field. We show that the number of sign reversals increases as d decreases. These findings are in agreement with recent computer simulations and illustrate the relevance of the different characteristic lengths for the vortex rectification effects. [less ▲]

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See detailOptimization of superconducting critical parameters by tuning the size and magnetization of arrays of magnetic dots
Silhanek, Alejandro ULg; Gillijns, W.; Milosevic, M. V. et al

in Physical Review. B, Condensed Matter and Materials Physics (2007), 76(10),

We investigate the nucleation of superconductivity in an Al film deposited on top of an array of micromagnets with perpendicular anisotropy by dc transport measurements. The absolute control of the ... [more ▼]

We investigate the nucleation of superconductivity in an Al film deposited on top of an array of micromagnets with perpendicular anisotropy by dc transport measurements. The absolute control of the magnetic state of the ferromagnets enabled us to explore the superconductor-normal-metal phase boundary as a function of the magnetization M of the dots. For a given external homogeneous field H, the magnetization of the dots can be tuned in such a way to optimize the field and current compensation in the sample, thus yielding a clear enhancement of the upper critical field H-c2. In addition, we theoretically demonstrate that the critical current I-c for a given temperature could be further enhanced by properly adjusting the size of the magnetic dots. These results are fully corroborated by the Ginzburg-Landau theory as well as analytic estimates. [less ▲]

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See detailMagnetic confinement of the superconducting condensate in superconductor-ferromagnet hybrid composites
Gillijns, W.; Aladyshkin, A Yu; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2007), 76(6),

The influence of an inhomogeneous magnetic field on the magnetoresistance of thin Al films, used in different superconductor-ferromagnet hybrids, has been investigated. Two contrasting magnetic textures ... [more ▼]

The influence of an inhomogeneous magnetic field on the magnetoresistance of thin Al films, used in different superconductor-ferromagnet hybrids, has been investigated. Two contrasting magnetic textures with out-of-plane magnetization are explored: namely, (i) a plain film in a multidomain state and (ii) an array of microsized dots. The stray fields of the ferromagnetic structures confine the superconducting condensate and, accordingly, modify the condition for the nucleation of superconductivity. By switching between different magnetic states of the ferromagnet, this confinement can be tuned at will, thereby reversibly changing the dependence of the critical temperature T-c on an external magnetic field H. In particular, continuous evolution from a conventional linear T-c(H) dependence with a single maximum to a reentrant superconducting phase boundary with multiple T-c peaks has been demonstrated. [less ▲]

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See detailEnhanced vortex trapping by a composite antidot lattice in a superconducting Pb film
Silhanek, Alejandro ULg; Van Look, L.; Jonckheere, R. et al

in Physica C: Superconductivity (2007), 460

Using electrical transport measurements, we study a composite antidot lattice consisting of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. We show ... [more ▼]

Using electrical transport measurements, we study a composite antidot lattice consisting of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. We show that placing an additional small antidot in the unit cell of the array a higher number of flux quanta per unit cell can be trapped inside the antidots, compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailSuperconducting microrings as magnetic pinning centers
Gillijns, W.; Silhanek, Alejandro ULg; Moshchalkov, V. V.

in Applied Physics Letters (2007), 91(20),

The nucleation of the superconducting condensate in an Al film deposited on top of a periodic array of microsized Pb rings is investigated using transport measurements. We demonstrate that these Pb rings ... [more ▼]

The nucleation of the superconducting condensate in an Al film deposited on top of a periodic array of microsized Pb rings is investigated using transport measurements. We demonstrate that these Pb rings form tunable pinning sites which can be switched at will to repel or attract vortices in the Al film, depending on their magnetic history. After zero field cooling, a repulsive interaction between the rings and the vortices is observed, while after field cooling, the interaction becomes attractive. The flexibility of such current-induced pinning centers can lead to an enhanced control over the vortex motion. (c) 2007 American Institute of Physics. [less ▲]

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See detailManipulation of the vortex motion in nanostructured ferromagnetic/superconductor hybrids
Silhanek, Alejandro ULg; Gillijns, W.; Moshchalkov, V. V. et al

in Applied Physics Letters (2007), 90(18),

The authors investigate the rectified motion of vortices in superconducting films deposited on top of a close-packed array of open in-plane magnetized triangular micromagnets. The dc voltage induced by ... [more ▼]

The authors investigate the rectified motion of vortices in superconducting films deposited on top of a close-packed array of open in-plane magnetized triangular micromagnets. The dc voltage induced by the vortex drift under an ac excitation is recorded for three different magnetic configurations of the triangles. When the magnetic elements are in the as-grown state a rectification signal which reverses sign when the field changes polarity is observed. In contrast to that, when the array of triangles is magnetized the observed rectification effect is independent of the field polarity and can be reverted by reorienting the magnetization of the micromagnets. (C) 2007 American Institute of Physics. [less ▲]

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See detailCrossover from intravalley to intervalley vortex motion in type-II superconductors with a periodic pinning array
Raedts, S.; Silhanek, Alejandro ULg; Moshchalkov, V. V. et al

in Physical Review. B : Condensed Matter (2006), 73(17),

We have determined the transition from intravalley vortex motion (Campbell regime) to intervalley motion (critical state regime) in Pb thin films with and without a square array of holes (antidots) by ... [more ▼]

We have determined the transition from intravalley vortex motion (Campbell regime) to intervalley motion (critical state regime) in Pb thin films with and without a square array of holes (antidots) by means of ac susceptibility chi(T,H) measurements. The Campbell regime is characterized by a maximum dissipation chi(')(max) dependent on the ac excitation h but nearly temperature independent. In contrast, in the critical state regime, the height of the dissipation peak remains constant, whereas its position shifts to lower temperatures with increasing h. We introduce an alternative way for determining the temperature dependence of the ac onset of the Bean critical state by analyzing the critical current density J(T) extracted from the chi(')(T) data at several h. We demonstrate that the presence of a periodic pinning array strongly affects the extension of the crossover area in the h-T diagram between these regimes. We show that this effect can be ascribed to the lower dispersion of the pinning energy together with the higher topological order for the antidot sample. [less ▲]

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See detailTunable field-induced superconductivity
Gillijns, W.; Silhanek, Alejandro ULg; Moshchalkov, V. V.

in Physical Review. B : Condensed Matter (2006), 74(22),

We investigate the transport properties of a thin superconducting Al layer covering a square array of magnetic dots with out-of-plane magnetization. A thorough characterization of the magnetic properties ... [more ▼]

We investigate the transport properties of a thin superconducting Al layer covering a square array of magnetic dots with out-of-plane magnetization. A thorough characterization of the magnetic properties of the dots allowed us to fine-tune their magnetic state at will, hereby changing the influence of the dots on the superconductor in a continuous way. We show that even though the number of vortex-antivortex pairs discretely increases with increasing the magnetization of the dots, no corresponding discontinuity is observed in the resistance of the sample. The evolution of the superconducting phase boundary as the magnetic state of the dots is swept permits one to devise a fully controllable and erasable field-induced superconductor. [less ▲]

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See detailTunable pinning in superconducting films with magnetic microloops
Silhanek, Alejandro ULg; Gillijns, W.; Moshchalkov, V. V. et al

in Applied Physics Letters (2006), 89(18),

The authors study the flux pinning properties of superconductor/magnetic microring lattice hybrid structures. The used open triangular micromagnets represent an eightfold degree of freedom system, with ... [more ▼]

The authors study the flux pinning properties of superconductor/magnetic microring lattice hybrid structures. The used open triangular micromagnets represent an eightfold degree of freedom system, with six polarized and two flux-closure possible states. By conveniently choosing the magnetic state of the underlying rings, it is possible to induce different pinning potentials. They show that the magnetic vortex state with minimum stray field produces a weaker pinning in comparison with the polarized states. (c) 2006 American Institute of Physics. [less ▲]

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See detailEnhanced pinning and proliferation of matching effects in a superconducting film with a Penrose array of magnetic dots
Silhanek, Alejandro ULg; Gillijns, W.; Moshchalkov, V. V. et al

in Applied Physics Letters (2006), 89(15),

The vortex dynamics in superconducting films deposited on top of a fivefold Penrose array of magnetic dots is studied by means of transport measurements. The authors show that in the low pinning regime ... [more ▼]

The vortex dynamics in superconducting films deposited on top of a fivefold Penrose array of magnetic dots is studied by means of transport measurements. The authors show that in the low pinning regime (demagnetized dots) a few periodic and aperiodic matching features coexist. In the strong pinning regime (magnetized dots) a richer structure of unforeseen periodic and aperiodic vortex patterns appear, giving rise to a clear enhancement of the critical current in a broader field range. Possible stable vortex configurations are determined by molecular dynamics simulations. (c) 2006 American Institute of Physics. [less ▲]

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See detailEnhanced vortex pinning by a composite antidot lattice in a superconducting Pb film
Silhanek, Alejandro ULg; Van Look, L.; Jonckheere, R. et al

in Physical Review. B : Condensed Matter (2005), 72(1),

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots ... [more ▼]

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots) substantially increase the critical temperature T-c(H) and critical current I-c(H) for all fields. Using electrical transport measurements, we study the effect of placing an additional small antidot in the unit cell of the array. This composite antidot lattice consists of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. The smaller antidots are located at the centers of the cells of the large antidots array. We show that the composite antidot lattice can trap a higher number of flux quanta per unit cell inside the antidots compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. Finally, the possible stable vortex lattice patterns at several matching fields are determined by molecular-dynamics simulations. [less ▲]

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See detailDendritic flux penetration in Pb films with a periodic array of antidots
Menghini, M.; Wijngaarden, R. J.; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2005), 71(10),

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows us to ... [more ▼]

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows us to identify a rich morphology of flux penetration patterns. We determine the phase boundary H-*(T) between dendritic penetration at low temperatures and a smooth flux invasion at high temperatures and fields. For the whole range of fields and temperatures studied, guided vortex motion along the principal axes of the square pinning array is clearly observed. In particular, the branching process of the dendrite expansion is fully governed by the underlying pinning topology. A comparative study between macroscopic techniques and direct local visualization sheds light onto the puzzling T- and H-independent magnetic response observed at low temperatures and fields. Finally, we find that the distribution of avalanche sizes at low temperatures can be described by a power law with exponent tau similar to 0.9(1). [less ▲]

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See detailVortex-antivortex dynamics and field-polarity-dependent flux creep in hybrid superconductor/ferromagnet nanostructures
Lange, M.; Van Bael, M. J.; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2005), 72(5),

Vortex-antivortex arrays (VAA) that are created in a type-II superconducting film by lattices of ferromagnetic dots with perpendicular anisotropy have been investigated. The highest critical current is ... [more ▼]

Vortex-antivortex arrays (VAA) that are created in a type-II superconducting film by lattices of ferromagnetic dots with perpendicular anisotropy have been investigated. The highest critical current is shifted to a nonzero value of the applied field, and current-voltage characteristics show different regimes of vortex motion even in zero-applied field due to the presence of the VAA. Creep of interstitial vortices is observed at low driving forces. This flux creep is strongly field-polarity dependent. [less ▲]

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See detailFlux-pinning properties of superconducting films with arrays of blind holes
Raedts, S.; Silhanek, Alejandro ULg; Van Bael, M. J. et al

in Physical Review. B : Condensed Matter (2004), 70(2),

We performed ac susceptibility measurements to explore the vortex dynamics and the flux-pinning properties of superconducting Pb films with an array of microholes (antidots) and not fully perforated holes ... [more ▼]

We performed ac susceptibility measurements to explore the vortex dynamics and the flux-pinning properties of superconducting Pb films with an array of microholes (antidots) and not fully perforated holes (blind holes). A lower ac shielding together with a smaller extension of the linear regime for the lattice of blind holes indicates that these centers provide a weaker pinning potential than antidots. Moreover, we found that the maximum number of flux quanta trapped by a pinning site, i.e., the saturation number n(s), is lower for the blind hole array. [less ▲]

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See detailExperimental determination of the number of flux lines trapped by microholes in superconducting samples
Silhanek, Alejandro ULg; Raedts, S.; Van Bael, M. J. et al

in Physical Review. B : Condensed Matter (2004), 70(5),

The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac susceptibility measurements. For different amplitudes h of the ac drive, the ac ... [more ▼]

The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac susceptibility measurements. For different amplitudes h of the ac drive, the ac susceptibility chi=chi'+ichi" exhibits a complex field dependence associated with different dynamic regimes. At very low ac drives where both multiquanta vortices trapped by the antidots and interstitial vortices oscillate inside the pinning potential (intravalley motion), a small kink in chi'(H) together with a very low dissipation is observed. At intermediate ac excitations such that vortices in the antidots remain pinned, whereas interstices are driven out of the pinning well, a more pronounced kink in the screening coinciding with the onset of dissipation [chi"(H)not equal0] indicates the entrance of interstitial vortices. Eventually, at high enough amplitudes all vortices are set in motion and the penetration of interstitial vortices appears as a sudden reduction of the shielding power. We show that these distinctive features allow us to identify clearly the maximum number of flux quanta per hole, regardless of the vortex dynamic regime. [less ▲]

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