References of "Silhanek, Alejandro"
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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 detailPhysical properties at high magnetic fields in CeIn2.75Sn0.25
Ebihara, T.; Harrison, N.; Jaime, M. et al

in Journal of Magnetism & Magnetic Materials (2007), 310(2), 298-299

High magnetic field induces quantum criticality in CeIn3 with suppressing the Neel temperature. Estimated quantum critical. efield of CeIn3 is about 60T where the Neel temperature is suppressed to reach ... [more ▼]

High magnetic field induces quantum criticality in CeIn3 with suppressing the Neel temperature. Estimated quantum critical. efield of CeIn3 is about 60T where the Neel temperature is suppressed to reach absolute zero. The magnetic. field (60T) is too high to measure electrical resistivity or specific heat precisely. Sn doping to In site of CeIn3 reduces the Neel temperature. Reduction of Neel temperature indicates lower critical. field to facilitate investigation of electronic states at high magnetic. fields. Electrical resistivity and specific. c heat in CeIn2.Sn-85(0.25) were measured to map an H-T phase diagram. (c) 2006 Elsevier B. V. All rights reserved. [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 detailIrreversible dynamics of the phase boundary in U(Ru(0.96)Rh(0.04))(2)Si(2) and implications for ordering
Silhanek, Alejandro ULg; Jaime, M.; Harrison, N. et al

in Physical Review Letters (2006), 96(13),

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru(0.96)Rh ... [more ▼]

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru(0.96)Rh(0.04))(2)Si(2), which yield irreversible properties similar to those at the valence transition of Yb(1-x)Y(x)InCu(4). To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition. [less ▲]

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See detailNonlocal magnetic field-tuned quantum criticality in cubic CeIn3-xSnx (x=0.25)
Silhanek, Alejandro ULg; Ebihara, Takao; Harrison, N. et al

in Physical Review Letters (2006), 96(20),

We show that antiferromagnetism in lightly (approximate to 8%) Sn-doped CeIn3 terminates at a critical field mu H-0(c)=42 +/- 2 T. Electrical transport and thermodynamic measurements reveal the effective ... [more ▼]

We show that antiferromagnetism in lightly (approximate to 8%) Sn-doped CeIn3 terminates at a critical field mu H-0(c)=42 +/- 2 T. Electrical transport and thermodynamic measurements reveal the effective mass m(*) not to diverge, suggesting that cubic CeIn3 is representative of a critical spin-density wave (SDW) scenario, unlike the local quantum critical points reported in anisotropic systems such as CeCu6-xAux and YbRh2Si2-xGex. The existence of a maximum in m(*) at a lower field mu H-0(x)=30 +/- 1 T may be interpreted as a field-induced crossover from local moment to SDW behavior as the Neel temperature falls below the Fermi temperature. [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 detailLattice involvement in low temperature phase of U(Ru,Rh)(2)Si-2
Jaime, M.; Silhanek, Alejandro ULg; Kim, K. H. et al

in Physica B: Condensed Matter (2006), 378-80

Specific heat, magnetocaloric effect and magnetization experiments were performed on the 5f-electron system U(Ru0.96Rh0.04)(2)Si-2. This compound exhibits a non-magnetic ground state with a single ... [more ▼]

Specific heat, magnetocaloric effect and magnetization experiments were performed on the 5f-electron system U(Ru0.96Rh0.04)(2)Si-2. This compound exhibits a non-magnetic ground state with a single magnetic field-induced phase between H = 26 and 38 T. We show that the transition into this phase is first-order as revealed by a large irreversible specific heat anomaly and asymmetric magnetocaloric effect. A comparative analysis with the valence transition compound YbInCu4, where similar irreversibility and asymmetry exists, is presented. (c) 2006 Published by Elsevier B.V. [less ▲]

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See detailGamma(5) quasiparticles and avoided quantum criticality in U(Ru,Rh)(2)Si-2
Silhanek, Alejandro ULg; Harrison, N.; Batista, C. D. et al

in Physica B: Condensed Matter (2006), 378-80

We discuss recent specific heat data in high magnetic fields on URu2Si2 and 4% Rh-doped URu2Si2 as well as previously published de Haas-van Alphen data at lower magnetic fields in pure URu2Si2: both of ... [more ▼]

We discuss recent specific heat data in high magnetic fields on URu2Si2 and 4% Rh-doped URu2Si2 as well as previously published de Haas-van Alphen data at lower magnetic fields in pure URu2Si2: both of which are consistent with quasiparticle bands formed from a hybridization between 5f-electron Gamma(5) doublets and regular conduction electrons. The system exhibits itinerant electron metamagnetism that gives rise to a putative quantum critical point at similar to 34-37T (depending on the % of Rh) that is subsequently unstable to field-induced phases. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailApproaching field tuned quantum criticality in CeIn3-xSnx
Silhanek, Alejandro ULg; Zocco, D.; Harrison, N. et al

in Physica B: Condensed Matter (2006), 378-80

We report on the magnetic field evolution of the Neel temperature T-N in the heavy electron system CeIn3-xSnx (x = 0 and 0.3), as determined by specific heat, magnetocaloric effect, and electrical ... [more ▼]

We report on the magnetic field evolution of the Neel temperature T-N in the heavy electron system CeIn3-xSnx (x = 0 and 0.3), as determined by specific heat, magnetocaloric effect, and electrical transport measurements. For the stoichiometric compound, T-N is fully suppressed at H-c similar to 65 T, whereas for x = 0.3 the critical field extrapolates to H-c similar to 30 T. An increasing Sommerfeld coefficient gamma, obtained above T-N, as field increases is observed and could be related to the a putative quantum critical point at H-c. (c) 2006 Published by Elsevier B.V. [less ▲]

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See detailAnisotropic avalanches and flux penetration in patterned superconductors
Gheorghe, D. G.; Menghini, M.; Wijngaarden, R. J. et al

in Physica C: Superconductivity (2006), 437-38

Both for a fundamental understanding of the flux penetration process and for technical applications, the role of artificial pinning sites (such as antidots) in superconductors generates a lot of interest ... [more ▼]

Both for a fundamental understanding of the flux penetration process and for technical applications, the role of artificial pinning sites (such as antidots) in superconductors generates a lot of interest. We perform magneto-optical imaging experiments on type-II Pb thin films patterned with square arrays of square antidots and square arrays of rectangular antidots and blind holes. We demonstrate that a square lattice of rectangular antidots can lead to similar anisotropy in flux penetration and critical current as a rectangular lattice of square antidots. In addition we show how thermo-magnetic avalanches can be guided-and hence to a certain extend controlled-by such holes. (c) 2006 Elsevier B.V. All rights reserved. [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 detailQuantum critical 5f electrons avoid singularities in U(Ru,Rh)(2)Si-2
Silhanek, Alejandro ULg; Harrison, N.; Batista, C. D. et al

in Physical Review Letters (2005), 95(2),

We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m)similar to 34 T, revealing striking similarities to the isotructural ... [more ▼]

We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m)similar to 34 T, revealing striking similarities to the isotructural Ce analog CeRu2Si2 for H > H-m. This suggests that strongly renormalized hybridized-band models apply equally well to both systems. The vanishing bandwidths as H -> H-m are consistent with a quantum-critical point close to H-m. The existence of a phase transition into an ordered phase in the vicinity of H-m for 4% Rh-doped URu2Si2, but not for CeRu2Si2, is consistent with a stronger superexchange in the case of the U 5f system. Irreversible processes at the transition indicate a strong coupling of the 5f orbitals to the lattice, most suggestive of electric quadrupolar order. [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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See detailParamagnetic reentrance of ac screening: Evidence of vortex avalanches in Pb thin films
Silhanek, Alejandro ULg; Raedts, S.; Moshchalkov, V. V.

in Physical Review. B : Condensed Matter (2004), 70(14),

We have studied the influence of a square array of pinning centers on the dynamics of vortex avalanches in Pb thin films by means of ac- and dc-magnetization measurements. Close to the superconducting ... [more ▼]

We have studied the influence of a square array of pinning centers on the dynamics of vortex avalanches in Pb thin films by means of ac- and dc-magnetization measurements. Close to the superconducting transition T-c, the commensurability between the vortex lattice and the pinning array leads to the well known local increments of the critical current. As temperature T decreases, matching features progressively fade out and eventually disappear. Further down in temperature, vortex avalanches develop and dominate the magnetic response. These avalanches manifest themselves as jumps in the dc magnetization and produce a lower ac shielding, giving rise to a paramagnetic reentrance in the ac screening chi(')(T). Within the flux-jump regime, two subregimes can be identified. Close to the boundary where vortex avalanches develop, the field separation between consecutive jumps follows the periodicity of the pinning array and a field- and temperature-dependent screening is observed. In this regime, the response also depends on frequency f in agreement with theoretical models for magnetothermal instabilities. At low enough temperatures and fields, the screening saturates to a constant value independent of T, H, and f, where jumps are randomly distributed. We have also found that vortex instabilities occupy a larger portion of the H-T diagram in patterned samples than in films without nanoengineered pinning sites. Finally, we discuss the possible origin of the vortex avalanches and compare our results with previous experimental and theoretical studies. [less ▲]

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