Alcalde Bessia, F., D. Flandre, N. André, J. Irazoqui, M. Pérez, M. Gómez Berisso, and J. Lipovetzky. "Ultra Low Power Ionizing Dose Sensor Based on Complementary Fully Depleted MOS Transistors for Radiotherapy Application." IEEE Transactions on Nuclear Science (2019): 1.
Abstract: We evaluate the use of the thick buried oxide (BOX) of Fully Depleted Silicon-on-Insulator (FD-SOI) transistors for Total Ionizing Dose (TID) measurements in a radiotherapy application. The devices were fabricated with a custom process in UniversitC) Catholique de Louvain (UCL) which allows to make accumulation mode PMOS transistors and inversion mode NMOS transistors. We characterized the temperature behavior of these devices and the response under X-ray radiation produced by an Elekta radiotherapy linear accelerator, and compared the obtained dose sensitivity to other published works. Taking advantage of these devices, an ultra low power MOS ionizing dose sensor, or MOS dosimeter, with inherent temperature compensation is presented. This dosimeter achieved a sensitivity of 154 mV/Gy with a temperature error factor of 13 mGy/°C and a current consumption below 1 nA.
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Ale Crivillero, M. V., M. L. Amigó, N. Haberkorn, G. Nieva, and J. Guimpel. "Microstructural control of the transport properties of β-FeSe films grown by sputtering." Journal of Applied Physics 126, no. 11 (2019): 115303.
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Ale Crivillero, M. V., N. Haberkorn, G. Nieva, and J. Guimpel. "Electrical transport properties of FeSe/Fe3O4 bilayers." Materials Today: Proceedings 14 (2019): 18–21.
Abstract: In this work, we study the electronic properties of FeSe/Fe3O4 bilayers deposited onto SrTiO3 (100) and MgO (100) substrates by DC magnetron sputtering. The comparative study of Fe3O4 films grown on SrTiO3 and MgO reveals significant differences in the intensity of the Verwey transition (Tv∼130K). This allows us to probe the impact of the distortions associated to the Verwey transition on the transport properties of the FeSe over-layer in the FeSe/Fe3O4 bilayers. A correlated increase in the resistance and weakened superconducting properties are observed..
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Aragón Sánchez, J., R. Cortés Maldonado, N. R. Cejas Bolecek, G. Rumi, P. Pedrazzini, M. I. Dolz, G. Nieva, C. J. van der Beek, M. Konczykowski, C. D. Dewhurst et al. "Unveiling the vortex glass phase in the surface and volume of a type-II superconductor." Communications Physics 2, no. 1 (2019): 143.
Abstract: Order-disorder transitions between glassy phases are common in nature and yet a comprehensive survey on the entailed structural changes is challenging since the constituents are in the micro-scale. Vortex matter in type-II superconductors is a model system where some of these experimental challenges can be tackled. Samples with point disorder present a glassy transition on increasing the density of vortices. A glassy yet quasi-crystalline phase, the Bragg glass, nucleates at low densities. The vortex glass stable at high densities is expected to be disordered, however its detailed structural properties remained experimentally elusive. Here we show that the vortex glass has large crystallites with in-plane positional displacements growing algebraically and short-range orientational order. Furthermore, the vortex glass has a finite and almost constant correlation length along the direction of vortices, in sharp contrast with strong entanglement. These results are important for the understanding of disorder-driven phase transitions in glassy condensed matter.
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Aragón Sánchez, J., R. Cortés Maldonado, M. I. Dolz, N. R. CejasBolecek, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Direct visualization of local interaction forces in Bi2Sr2CaCu2O8+δ vortex matter." Materials Today: Proceedings 14 (2019): 34–37.
Abstract: We study the local vortex-vortex interaction force fi of the structure frozen during a field-cooling process in an electron-irradiated Bi2Sr2CaCu2O8+δ sample. We compute this magnitude from snapshots of the vortex structure obtained via magnetic decoration experiments at various fields H in the same sample. Since the observed structures correspond to the equilibrium ones frozen at T∼Tirr(H)[1], at this temperature the local modulus of fi roughly equals the local pinning force at the decorated surface of the sample. We estimate the most probable local pinning force from the mode value of the fi(r)distribution, fpm. We found that fpm grows algebraically with H and in electron-irradiated samples is 50-20% smaller than for samples with columnar defects.
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Betancourth, D., V. F. Correa, J. I. Facio, Fernández J., V. Vildosola, R. Lora-Serrano, J. M. Cadogan, A. A. Aligia, P. S. Cornaglia, and García D.J. "Magnetostriction reveals orthorhombic distortion in tetragonal Gd compounds." Physical Review B 99 (2019): 134406.
Abstract: We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRh(In1−xCdx )5
(x = 0 and 0.025) single-crystal samples that show a sudden change in the dilation at a field B for temperatures
below the Néel transition temperature TN . We present a first-principles model including crystal-field effects,
dipolar and exchange interactions, and the dependence of the latter with lattice distortions in order to fully
account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows
that a transition between metastable states occurs at the field B. It also indicates that two degenerate phases
should coexist at temperatures below TN , which may explain the lack of observation, in high-resolution
x-ray experiments, of an orthorhombic distortion at the Néel transition, even though the experimentally
determined magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling from our model
is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the
same phenomenology.
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Correa V. F. "Introducing the Hamiltonian as a 'thermodynamic' potential." European Journal of Physics 40 (2019): 035007.
Abstract: A conceptually simple physical interpretation of a conserved Hamiltonian ïˆ
for a mechanical system with a time-dependent constraint is given. For the
case of a bead on a vertical hoop forced to rotate with constant angular
velocity w, ïˆ is nothing but the total energy of the system plus the external
actuator keeping ω fixed. In an analogy with thermodynamics, the Hamiltonian
is introduced as a thermodynamic potential obtained from a Legendre transformation
of the energy, in a very instructive way. The ideas can be made
extensive to different problems with time-dependent constraints.
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Correa, V. F., A. G. Villagrán Asiares, D. Betancourth, S. Encina, P. Pedrazzini, P. S. Cornaglia, García D.J., J. G. Sereni, B. Maiorov, N. Caroca-Canales et al. "Strong magnetoelastic effect in CeCo1−xFexSi as Néel order is suppressed." Physical Review B 100 (2019): 184409.
Abstract: A very strong magnetoelastic effect in the CeCo1−xFexSi alloys is reported. The strength of the magnetostrictive
effect can be tuned upon changing x. The moderate low-temperature linear magnetostriction observed at low
Fe concentrations becomes very large (L
L (16T, 2K) = 3 × 10−3) around the critical concentration xc ≈ 0.23 at
which the long-range antiferromagnetic order vanishes. Upon increasing doping through the nonmagnetic region
(x > xc), the magnetostriction strength gradually weakens again. The interplay between magnetic order and the
Kondo screening appears to cause an enhanced valence susceptibility slightly changing the Ce ions valence,
ultimately triggering the large magnetostriction observed around the critical concentration. Previous studies
of the evolution of the lattice parameters with x as well as magnetization and x-ray absorption spectroscopy
measurements support this hypothesis.
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Dolz, M. I., N. R. C. Bolecek, J. Puig, H. Pastoriza, G. Nieva, J. Guimpel, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Enhancement of penetration field in vortex matter in mesoscopic superconductors due to Andreev bound states." Physical Review B 100, no. 6 (2019): 064508.
Abstract: We study the field for the penetration of a first vortex, HP, for vortex matter nucleated in micron-sized samples with edges aligned along the nodal and antinodal directions of the d-wave superconducting order parameter of Bi2Sr2CaCu2O8−δ. Here we present evidence that the HP for vortex matter nucleated in mesoscopic samples with edges parallel to the nodal direction is larger than for the antinodal case, ∼72% at low temperatures. This finding supports the theoretical proposal that surface Andreev bound states appearing in a sample with edges parallel to the nodal direction would produce an anomalous Meissner current that increases the Bean-Livingston barrier for vortex penetration.
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Gastaldo, F., S. Gabáni, A. Džubinská, M. Reiffers, G. PristáÅ¡, I. ÄŒurlík, P. Skyba, M. Clovecko, F. Vavrek, J. G. Sereni et al. "YbPd2In: A promising candidate for strong entropy accumulation at very low temperature." Physical Review B 100, no. 17 (2019): 174422.
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Haberkorn N, Guimpel J., Suárez S, Lee Jae-Hun, Lee Hunju and Moon S H. "Competition between pinning produced by extrinsic random point disorder and superconducting thermal fluctuations in oxygen-deficient GdBa2Cu3O x coated conductors." Superconductor Science and Technology 32 (2019): 125015.
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Haberkorn N. "Fabrication of β-Mo2C ultra-thin films by thermal annealing of molybdenum/carbon heterostructures." Materials Letters X 1 (2019): 100004.
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Haberkorn N., Suárez S., Lee Jae-Hun, Moon S. H. and Lee Hunju. "In-field dependences of the critical current density Jc in GdBa2Cu3O7-d coated conductors produced by Zr irradiation and post-annealing at low temperatures." Solid State Communications 289 (2019): 51–55.
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Haberkorn N., Xu M., Meier W. R., Schmidt J., Bud’ko S. L, Canfield P. C. "Effect of Ni doping on vortex pinning in CaK(Fe1-xNix)4As4 single crystals." Physical Review B 100 (2019): 064524.
Abstract: We study the correlation between chemical composition and vortex dynamics in Ni-doped CaK(Fe1−xNix)4As4 (x=0, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities Jc and the flux creep rates S. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent μ within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (U0 <100 K). The undoped crystals display modest
Jc values at low temperatures and high magnetic fields applied along the c-axis. Jc (T) dependences at high fields display an unusual peak. The enhancement in Jc(T) matches with an increase in U0 and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in Tc there is a nonmonotonic change in Jc. Initially
Jc increases, reaching a maximum value for x = 0.015, and then Jc decreases for x ≥ 0.025. This change in Jc (x) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of Jc(H) also manifests a change in behavior between these x values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent μ with Ni content, x. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation.
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Haberkorn, N., S. Bengio, S. Suárez, P. D. Pérez, J. A. Hofer, and M. Sirena. "Effect of thermal annealing and irradiation damage on the superconducting critical temperature of nanocrystalline γ-Mo2N thin films." Materials Letters 236 (2019): 252–255.
Abstract: We report on the influence of the disorder and stoichiometry in the resulting superconducting critical temperature of γ-Mo2N thin films. Initially, three films (with Tc values of 7.6 K, 6.8 K and 6 K) were grown at room temperature by reactive sputtering, on Si (1 0 0) using different N2/(Ar+N2) mixtures. The influence of the thermal annealing up to 973 K and irradiation damage produced by 1 MeV Zr+(fluence up 2 × 1014 cm−2) is analyzed. The Tc of pristine films remains unchanged for increasing irradiation doses up 2 × 1014 cm−2. The Tc for annealed films decreases close to the value expected for bulk samples (≈5 K) for increasing the annealing temperature. Successive irradiations of the annealed films tend to increase their Tc up to its initial values (before annealing). The results indicate that the Tc in nanometric grain size γ-Mo2N thin films is affected by both nitrogen stoichiometry and disorder at the atomic scale.
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Hofer J. A., Haberkorn N. "Superconductivity in nanocrystalline tungsten thin films growth by sputtering in a nitrogen-argon mixture." Thin Solid Films 685 (2019): 117–122.
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Kneidinger, F., I. Zeiringer, A. Siderenko, E. Bauer, H. Michor, P. Rogl, and J. G. Sereni. "Physical properties of CeIrSi with trillium-lattice frustrated magnetism." Physical Review B 100, no. 13 (2019): 134442.
Abstract: Magnetic (χ), transport (Ï), and heat capacity (Cm) properties of CeIrSi are investigated to elucidate the effect of geometric frustration in this compound with trillium type structure because, notwithstanding its robust effective moment,
μeff≈2.46μB, this Ce-lattice compound does not undergo a magnetic transition. In spite of that it shows broad Cm(T)/T and χ(T) maxima centered at Tmax≈1.5 K, while a ÏâˆT2 thermal dependence, characteristic of electronic spin coherentfluctuations,is observed below Tcoh≈2.5 K. Magnetic field does not affect significantly the position of the mentioned maxima up to ≈1 T, though χ(T) shows an incipient structure that completely vanishes at
μ0H≈1 T. Concerning the ÏâˆT2 dependence, it is practically not affected by magneticfield up to μ0H=9 T, with the residual resistivity Ï0(H) slightlydecreasing and Tcoh(H) increasing. These results are compared with thephysical properties observed in other frustrated intermetallic compound.
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Morán M., Condó A. M., Bengio S., Soldera F., Sirena M. and Haberkorn N. "Martensitic transformation in free-standing Cu-Al-Ni thin films with micrometric grain size." Materials Research Express 6 (2019): 096556.
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Morán M., Condó A. M., Soldera F., Sirena M. and Haberkorn N. "Thickness dependence of the martensitic transformation in textured Cu-Al-Ni thin films grown by sputtering on Si (001)." Materials Today: Proceedings 14 (2019): 96–99.
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Morán M., Condó A. M., Suarez S., Soldera F., Haberkorn N. "Ion implantation inducing two-way shape memory effect in Cu-Al-Ni thin films." Materials Letters 255 (2019): 126569.
Abstract: We report two-way shape memory effect (TWSME) induced by Al ion implantation in 6 μm thick Cu-Al-Ni thin films. The films display an average grain size of 3.7 μm and a martensitic transformation temperature (MS) of ≈ 240 K. The film was irradiated with 2 MeV Al ions with a fluence of 6 × 10^15 ion.cm−2 (penetration distance up to ≈ 1.1 μm). After irradiation, the film displays well defined TWSME with a radius of curvature of ≈ 1 mm. The results indicate that the irradiation produces mainly changes in the austenitic order.
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Rumi, G., L. J. Albornoz, P. Pedrazzini, M. I. Dolz, H. Pastoriza, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+δ with columnar defects." Materials Today: Proceedings 14 (2019): 30–33.
Abstract: We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi2Sr2CaCu2O8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, TFOT, in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus TFOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.
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Rumi, G., J. Aragón Sánchez, F. Elías, R. Cortés Maldonado, J. Puig, N. R. Cejas Bolecek, G. Nieva, M. Konczykowski, Y. Fasano, and A. B. Kolton. "Hyperuniform vortex patterns at the surface of type-II superconductors." Physical Review Research 1, no. 3 (2019): 033057.
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Sereni, J. G. "Analysis of Entropy trajectories in very Heavy Fermions for Adiabatic Demagnetization Refrigeration at the T<1K range." Materials Today: Proceedings 14 (2019): 67–71.
Abstract: With the aim to improve classical paramagnetic salts performances for adiabatic magnetization refrigeration processes, relevant thermodynamic parameters of recently discovered very heavy fermion Yb-based intermetallic compounds are investigated within the sub-Kelvin range of temperature. Focusing on fixed thermal points, required for e.g. photonic devices operating within the 100 mK range in orbital satellites, the nature of respective magnetic ground states are discussed together with the effect of an 'entropy bottleneck' imposed by the Nernst postulate the entropy S(T) trajectories. To gain insight into the main criteria for a proper choice of suitable materials for alternative applications, thermomagnetic S(T,B) trajectories and respective derivatives: δS/δT and δS/δB, are analyzed as key parameters for this magnetocaloric process and compared with those from the classical salt Cerium-Magnesium-Nitride (CMN).
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Sereni, J. G., J. Roberts, F. Gastaldo, and M. Giovannini. "Suppression of the Shastry-Sutherland phase driven by electronic concentration reduction in magnetically frustrated Ce2.15Pd1.95(Sn1-yIny)0.9 alloys." Physical Review B 100, no. 5 (2019): 054421.
Abstract: Exploiting the possibility to switch from antiferromagnetic (AFM) and ferromagnetic (FM) ground states (GSs) in out-stoichiometric branches of
Ce2Pd2In alloys, the stability of Shastry-Sutherland (ShSu) phase of
Ce2Pd2Sn as a function of Sn/In electron doping was studied. Magnetic and specific-heat measurements show that the Ce-rich compositions stabilize the FM-GS throughout the Sn/In-FM substitution, allowing to extend the formation of the ShSu phase up to its collapse in a tricritical point around ycr=0.5. On the other hand, this behavior is quite different from that reported in a recent investigation on the AFM branch where atomic disorder at intermediate Sn/In-AFM concentrations inhibits the formation of the ShSu phase.
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Sereni, J. G., J. Roberts, F. Gastaldo, M. Gómez Berisso, and M. Giovannini. "Shastry-Sutherland phase formation in magnetically frustrated Ce2Pd2In1-xSnx alloys." Materials Today: Proceedings 14 (2019): 80–83.
Abstract: Taking profit that the ternary indides Ce2+εPd2-εIn form two branches of solid solutions allowing to access to ferromagnetic (FM, ε > 0) or anti-ferromagnetic (AFM, ε < 0) ground states depending on the relative Ce/Pd concentration 'ε' , we have tested the possibility of a Shastry-Sutherland phase formation by electron doping the trivalent In lattice with tetravalent Sn. Starting from the AFM, ε < 0 side provides the lowest electron concentration conditions increasing the sensitivity to electron doping. For such a purpose low temperature thermal and magnetic properties were investigated on Ce2+εPd2-εIn1-xSnx alloys within the 0 ≤ x ≤ 0.6 range of concentration.
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Zapata, C., G. Nieva, J. M. Ferreyra, M. Villafuerte, L. Lanoël, and G. Bridoux. "The s-d exchange model as the underlying mechanism of magnetoresistance in ZnO doped with alkali metals." Journal of Physics: Condensed Matter 31, no. 34 (2019): 345801.
Abstract: High field magnetoresistance has been studied in epitaxial n-type ZnO:Na and ZnO:Li thin films in a temperature range between 4 K and 150 K. The resulting negative magnetoresistance can be well fitted using a semiempirical model of Khosla and Fischer based on third order contributions to the s-d exchange Hamiltonian. The parameters obtained from this model were carefully analyzed. One of these parameters is related to a ratio between electron mobilities at zero field (a non-exchange scattering mobility and an exchange or spin dependent one ). From Hall effect measurements was obtained, displaying a weak temperature dependence in accordance with highly n-doped ZnO while the extracted exhibits an anomalous T-dependence. On the other hand, our magnetoresistance data cannot be properly fitted using Kawabata’s expression based on a weak-localization model.
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