Dynamic Regimes in Films with a Periodic Array of Antidots

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T,H) measurements. At low enough ac drive amplitudes h, vortices moving inside the pinning potential give rise to a frequency- and h-independent response together with a scarce dissipation. For higher amplitudes, the average distance travelled by vortices surpasses the pinning range and a critical state develops. We found that the boundary h*(H,T) between these regimes smoothly decreases as T increases whereas a step-like behavior is observed as a function of field. We demonstrate that these steps in h*(H) arise from sharp changes in the pinning strength corresponding to different vortex configurations. For a wide set of data at several fields and temperatures in the critical state regime, we show that the scaling laws based on the simple Bean model are satisfied.Comment: 7 pages, 5 figure

A new cluster-type statistical model for the prediction of deformation textures

An attempt was done to improve the quality of deformation texture predictions by statistical models through the introduction of "clusters" of N grains thus defining a third, intermediate length scale. The interaction between each cluster and the macroscopic length scale is of the Taylor type, whereas inside each cluster a VPSC scheme is used. Predictions of cold rolling deformation textures were quantitatively compared with experimental results for a steel alloy. The results are encouraging

Creation and pinning of vortex-antivortex pairs

Computer modeling is reported about the creation and pinning of a magnetic vortex-antivortex (V-AV) pair in a superconducting thin film, due to the magnetic field of a vertical magnetic dipole above the film, and two antidot pins inside the film. For film thickness $= 0.1\xi$, $\kappa = 2$, and no pins, we find the film carries two V-AV pairs at steady state in the imposed flux range $2.10\Phi_0 < \Phi^+ < 3.0\Phi_0$, and no pairs below. With two antidot pins suitably introduced into the film, a single V-AV pair can be stable in the film for $\Phi^+ \ge 1.3\Phi_0$. At pin separation $\ge 17\xi$, we find the V-AV pair remains pinned after the dipole field is removed, and, so can represent a 1 for a nonvolatile memory.Comment: 8 pages, 6 figure

Flux pinning properties of superconductors with an array of blind holes

We performed ac-susceptibility measurements to explore the vortex dynamics and the flux pinning properties of superconducting Pb films with an array of micro-holes (antidots) and non-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 ns, is lower for the blind hole array.Comment: 6 figures, 6 page

Phase diagram of a superconductor / ferromagnet bilayer

The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the critical temperature Tc of the superconductor in zero field is strongly reduced, and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For a very inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields, indicating a dimensional crossover from a one-dimensional network-like to a two-dimensional behavior in the nucleation of superconductivity.Comment: 6 pages, 7 figure

Magnetic nanoparticles as efficient bulk pinning centers in type-II superconductors

Enhancement of flux pinning by magnetic nanoparticles embedded into the bulk of type-2 superconductor is studied both theoretically and experimentally. Magnetic part of the pinning force associated with the interaction between a spherical magnetic inclusion and an Abrikosov vortex was calculated in the London approximation. Calculations are supported by the experimental results obtained on sonochemically modified MgB2 superconductor with embedded magnetic Fe2O3 nanoparticles and compared to MgB2 with nonmagnetic Mo2O5 pinning centers of similar concentration and particle size distribution. It is shown that ferromagnetic nanoparticles result in a considerable enhancement of vortex pinning in large-kappa type-2 superconductors.Comment: PDF, 14 page

Identifying single electron charge sensor events using wavelet edge detection

The operation of solid-state qubits often relies on single-shot readout using a nanoelectronic charge sensor, and the detection of events in a noisy sensor signal is crucial for high fidelity readout of such qubits. The most common detection scheme, comparing the signal to a threshold value, is accurate at low noise levels but is not robust to low-frequency noise and signal drift. We describe an alternative method for identifying charge sensor events using wavelet edge detection. The technique is convenient to use and we show that, with realistic signals and a single tunable parameter, wavelet detection can outperform thresholding and is significantly more tolerant to 1/f and low-frequency noise.Comment: 11 pages, 4 figure

Sorption heat storage for long-term low-temperature applications: A review on the advancements at material and prototype scale

Sorption heat storage has the potential to store large amounts of thermal energy from renewables and other distributed energy sources. This article provides an overview on the recent advancements on long-term sorption heat storage at material- and prototype- scales. The focus is on applications requiring heat within a temperature range of 30–150 °C such as space heating, domestic hot water production, and some industrial processes. At material level, emphasis is put on solid/gas reactions with water as sorbate. In particular, salt hydrates, adsorbents, and recent advancements on composite materials are reviewed. Most of the investigated salt hydrates comply with requirements such as safety and availability at low cost. However, hydrothermal stability issues such as deliquescence and decomposition at certain operating conditions make their utilization in a pure form challenging. Adsorbents are more hydrothermally stable but have lower energy densities and higher prices. Composite materials are investigated to reduce hydrothermal instabilities while achieving acceptable energy densities and material costs. At prototype-scale, the article provides an updated review on system prototypes based on the reviewed materials. Both open and closed system layouts are addressed, together with the main design issues such as heat and mass transfer in the reactors and materials corrosion resistance. Especially for open systems, the focus is on pure adsorbents rather than salt hydrates as active materials due to their better stability. However, high material costs and desorption temperatures, coupled with lower energy densities at typical system operating conditions, decrease their commercial attractiveness. Among the main conclusions, the implementation within the scientific community of common key performance indicators is suggested together with the inclusion of economic aspects already at material-scale investigations.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES