arXiv subjects

E. M. Gonzalez

Publications and source records attributed to E. M. Gonzalez.

At least 19 recordsLinked to original sources

arXiv2026

High-Pressure Reinforced Vessel, produced by Additive Manufacturing, to be used as a gas target for the measurement program at n_TOF -- Multiple Argon Experiments (MArEX)

The n_TOF collaboration has expressed interest in developing transmission experiments with liquid argon (LAr) and gaseous argon (GAr) to improve the understanding of neutron propagation and capture in Ar. This topic is relevant to both nuclear and particle physics, as LAr is widely used in neutrino experiments, dark matter searches and other applications. Despite its widespread use, neutron interactions on Ar are still poorly characterized. In this context, the Multiple Argon Experiments (MArEX) initiative aims to address these gaps by providing detailed measurements of neutron and Ar interactions, including resolved resonance parameters and radiative capture widths, across an unprecedented energy range from 1 eV to 200 MeV. As part of MArEX research activities, this paper presents the development of an innovative High-Pressure Reinforced Vessel (HPRV) for GAr targets, produced by Additive Manufacturing (AM) and reinforced with carbon fibre (CF). The experimental results confirmed the capability of the vessel to withstand high operating pressure without any issues and the capability of the Multi-layers Finite Element Model (MLs-FEM) to simulate and predict the stress behaviour and the operation limit of the vessel.

physics.ins-det↗

arXiv2023

Enhancement of vortex liquid phase and reentrant behavior in NiBi3 single crystals

We investigated the vortex phase diagram of needle shaped high quality NiBi3 single crystals by transport measurements. The current is applied along the crystalline b-axis of this intermetallic quasi-1D BCS superconductor. The single crystals show a Ginzburg-Levanchuk (Gi) parameter few orders of magnitude larger than other low Tc BCS superconductors. Vortex phase diagram, critical currents and pinning forces have been extracted from the experimental data. The main findings are: 1) Enhancement of the vortex liquid phase in comparison with low Tc superconductors, 2) reentrance of the liquid phase at low fields and 3) deviation of the pinning force vs field from the usual pinning mechanisms. The interplay between weak pinning, due to quenched disorder, and the quasi-1D character of the material could be a hint to explain the lack of a single pinning mechanism.

cond-mat.supr-con↗

arXiv2021

Realization of macroscopic ratchet effect based on nonperiodic and uneven potentials

Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin-ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In our case, the asymmetric potentials are provided by charged Néel walls located in the vertices of the magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to the magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, when they move with trajectories crossing charged Néel walls with different orientations. Moreover, the appropriate asymmetric pair potentials which generate the local ratchet effect have been identified. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes.

cond-mat.supr-con↗

arXiv2020

Little-Parks Effect Governed by Magnetic Nanostructures with Out-of-Plane Magnetization Little-Parks Effect Governed by Magnetic Nanostructures with Out-of-Plane Magnetization

Little-Parks effect names the oscillations in the superconducting critical temperature as a function of the magnetic field. This effect is related to the geometry of the sample. In this work, we show that this effect can be enhanced and manipulated by the inclusion of magnetic nanostructures with perpendicular magnetization. These magnetic nanodots generate stray fields with enough strength to produce superconducting vortex-antivortex pairs. So that, the L-P effect deviation from the usual geometrical constrictions is due to the interplay between local magnetic stray fields and superconducting vortices. Moreover, we compare our results with a low-stray field sample (i.e. with the dots in magnetic vortex state) showing how the enhancement of the L-P effect can be explained by an increment of the effective size of the nanodots.

cond-mat.supr-con↗

arXiv2019

Vortex dynamics controlled by local superconducting enhancement

A controlled local enhancement of superconductivity yields unexpected modifications in the vortex dynamics. This local enhancement has been achieved by designing an array of superconducting Nb nanostructures embedded in a V superconducting film. The most remarkable findings are: i) vanishing of the main commensurability effect between the vortex lattice and the array unit cell, ii) hysteretic behavior in the vortex dynamics, iii) broadening of the vortex liquid phase and iv) strong softening of the vortex lattice. These effects can be controlled and they can be quenched by reducing the Nb array superconducting performance applying an in-plane magnetic field. These results can be explained by taking into account the repulsive potential landscape created by the superconducting Nb nanostructures on which vortices move.

cond-mat.supr-con↗

arXiv2018

Magnetic order and disorder in nanomagnets probed by superconducting vortices

We have studied two nanomagnet systems with strong (Co/Pd multilayers) and weak (NdCo alloy films) stray magnetic fields by probing the out-of-plane magnetic states with superconducting vortices. The hybrid samples are made of array of nanomagnets embedded in superconducting Nb thin films. The vortex motion detects relevant magnetic state features, since superconducting vortices are able to discriminate between different magnetic stray field strengths and directions. The usual matching effect between the superconducting vortex lattice and the periodic pinning array can be quenched by means of disorder magnetic potentials with strong stray fields at random. Ordered stray fields retrieve the matching effect and yield asymmetry and shift in the vortex dissipation signal. Furthermore vortices can discriminate the sizes of the nanomagnet magnetic domains, detecting magnetic domain sizes as small as 70 nm. In addition, we observe that the vortex cores play the crucial role instead of the supercurrents around the vortex.

cond-mat.supr-con↗

arXiv2018

Topologically protected superconducting ratchet effect generated by spin-ice nanomagnets

We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin-ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin-ice rules, ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic Néel walls, iii) the interaction between superconducting vortices and the asymmetric potentials provided by the Néel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array.

cond-mat.supr-con↗

arXiv2017

Force-free state in a superconducting single crystal and angle-dependent vortex helical instability

Superconducting 2H-NbSe2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V, I) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular shape 2H-NbSe2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e. in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence.Moreover, this exponential dependence can be observed for in-plane applied magnetic fields up to 40 degrees off the current direction, which implies that the vortex helical instability plays a role in dissipation even out of the force-free configuration.

cond-mat.supr-con↗

arXiv2017

Different approaches to generate matching effects using arrays in contact with superconducting films

Superconducting films in contact with non-superconducting regular arrays can exhibit commensurability effects between the vortex lattice and the unit cell of the pinning array. These matching effects yield a slowdown of the vortex flow and the corresponding dissipation decrease. The superconducting samples are Nb films grown on Si substrates. We have studied these matching effects with the array on top, embedded or threading the Nb superconducting films and using different materials (Si, Cu, Ni, Py dots and dots fabricated with Co/Pd multilayers). These hybrids allow studying the contribution of different pinning potentials to the matching effects. The main findings are: i) Periodic roughness induced in the superconducting film is enough to generate resistivity minima; ii) A minor effect is achieved by magnetic pinning from periodic magnetic field potentials obtained by dots with out of plane magnetization grown on top of the superconducting film, iii) In the case of array of magnetic dots embedded in the films vortex flow probes the magnetic state; i.e. magnetoresistance measurements detect the magnetic state of very small nanomagnets. In addition, we have studied the role played by the local order in the commensurability effects. This was attained using an array that mimics a smectic crystal. We have found that preserving the local order is crucial. If the local order is not retained the magnetoresistance minima vanish.

cond-mat.supr-con↗

arXiv2016

Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects

In order to compare magnetic and non-magnetic pinning we have nanostructured two superconducting films with regular arrays of pinning centers: Cu (non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low applied magnetic fields, when all the vortices are pinned in the artificial inclusions, magnetic dots prove to be better pinning centers, as has been generally accepted. Unexpectedly, when the magnetic field is increased and interstitial vortices appear, the results are very different: we show how the stray field generated by the magnetic dots can produce an effective reduction of the penetration length. This results in strong consequences in the transport properties, which, depending on the dot separation, can lead to an enhancement or worsening of the transport characteristics. Therefore, the election of the magnetic or non-magnetic character of the pinning sites for an effective reduction of dissipation will depend on the range of the applied magnetic field.

cond-mat.supr-con↗

arXiv2016

Superconducting/magnetic three state nanodevice for memory and reading applications

We present a simple nanodevice that can operate in two modes: i) three-state memory and ii) reading device. The nanodevice is fabricated with an array of ordered triangular-shaped nanomagnets embedded in a superconducting thin film. The input signal is ac current and the output signal is dc voltage. Vortex ratchet effect in combination with out of plane magnetic anisotropy of the nanomagnets is the background physics which governs the nanodevice performance.

cond-mat.supr-con↗

arXiv2015

Experimental realization of smectic phase in vortex matter induced by symmetric potentials arranged in two-fold symmetry arrays

Smectic order has been generated in superconducting Nb films with two-fold symmetry arrays of symmetric pinning centers. Magnetic fields applied perpendicularly to the films develop a vortex matter smectic phase that is easily detected when the vortices commensurate with the pinning center array. The smectic phase can be turned on and off with external parameters.

cond-mat.supr-con↗

arXiv2014

Transverse ratchet effect and superconducting vortices: Simulation and experiment

A transverse ratchet effect has been measured in magnetic/superconducting hybrid films fabricated by electron beam lithography and magnetron sputtering techniques. The samples are Nb films grown on top of an array of Ni nanotriangles. Injecting an ac current parallel to the triangle reflection symmetry axis yields an output dc voltage perpendicular to the current, due to a net motion of flux vortices in the superconductor. The effect is reproduced by numerical simulations of vortices as Langevin particles with realistic parameters. Simulations provide an intuitive picture of the ratchet mechanism, revealing the fundamental role played by the random intrinsic pinning of the superconductor.

cond-mat.stat-mech↗

arXiv2014

Vortex pinning vs superconducting wire network: origin of periodic oscillations induced by applied magnetic fields in superconducting films with arrays of nanomagnets

Hybrid magnetic arrays embedded in superconducting films are ideal systems to study the competition between different physical (such as the coherence length) and structural length scales such as available in artificially produced structures. This interplay leads to oscillation in many magnetically dependent superconducting properties such as the critical currents, resistivity and magnetization. These effects are generally analyzed using two distinct models based on vortex pinning or wire network. In this work, we show that for magnetic dot arrays, as opposed to antidot (i.e holes) arrays, vortex pinning is the main mechanism for field induced oscillations in resistance R(H), critical current Ic(H), magnetization M(H) and ac-susceptibility Xac(H) in a broad temperature range. Due to the coherence length divergence at Tc, a crossover to wire network behavior is experimentally found. While pinning occurs in a wide temperature range up to Tc, wire network behavior is only present in a very narrow temperature window close to Tc. In this temperature interval, contributions from both mechanisms are operational but can be experimentally distinguished.

cond-mat.supr-con↗

arXiv2013

Control of dissipation in superconducting films by magnetic stray fields

Hybrid superconducting/magnetic nanostructures on Si substrates have been built with identical physical dimensions but different magnetic configurations. By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex state magnetic configurations, the stray fields are systematically tuned. Dissipation in the mixed state of superconductors can be decreased (increased) by several orders of magnitude by decreasing (increasing) the stray magnetic fields. Furthermore, ordering of the stray fields over the entire array helps to suppress dissipation and enhance commensurability effects increasing the number of dissipation minima.

cond-mat.supr-con↗

arXiv2011

Vortex ratchet reversal: The role of interstitial vortices

Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites.

cond-mat.supr-con↗

arXiv2010

Vortex ratchet reversal at fractional matching fields in kagomé-like array with symmetric pinning centers

Arrays of Ni nanodots embedded in Nb superconducting films have been fabricated by sputtering and electron beam lithography techniques. The arrays are periodic triangular lattices of circular Ni dots arranged in a kagomé-like pattern with broken reflection symmetry. Relevant behaviors are found in the vortex lattice dynamics : i) At values lower than the first integer matching field, several fractional matching fields are present when the vortex lattice moves parallel or perpendicular to the reflection symmetry axis of the array showing a clear anisotropic character in the magnetoresistance curves, ii) injecting an ac current perpendicular to the reflection symmetry axis of the array yields an unidirectional motion of the vortex lattice (ratchet effect) as a result of the interaction between the whole vortex lattice and the asymmetric lattice of dots, iii) increasing the input current amplitudes the ratchet effect changes polarity independently of matching field values. These experimental results can be explained taking into account the vortex lattice density.

cond-mat.supr-con↗

arXiv2010

Control of the chirality and polarity of magnetic vortices in triangular nanodots

Magnetic vortex dynamics in lithographically prepared nanodots is currently a subject of intensive research, particularly after recent demonstration that the vortex polarity can be controlled by in-plane magnetic field. This has stimulated the proposals of non-volatile vortex magnetic random access memories. In this work, we demonstrate that triangular nanodots offer a real alternative where vortex chirality, in addition to polarity, can be controlled. In the static regime, we show that vortex chirality can be tailored by applying in-plane magnetic field, which is experimentally imaged by means of Variable-Field Magnetic Force Microscopy. In addition, the polarity can be also controlled by applying a suitable out-of-plane magnetic field component. The experiment and simulations show that to control the vortex polarity, the out-of-plane field component, in this particular case, should be higher than the in-plane nucleation field. Micromagnetic simulations in the dynamical regime show that the magnetic vortex polarity can be changed with short-duration magnetic field pulses, while longer pulses change the vortex chirality.

cond-mat.mtrl-sci↗