Influence of nonlocal damping on the field-driven domain wall motion

We derive the complete expression of nonlocal damping in noncollinear magnetization due to the nonuniform spin current pumped by precessional magnetization and incorporate it into a generalized Thiele equation to study its effects on the dynamics of the transverse and vortex domain walls (DWs) in ferromagnetic nanowires. We demonstrate that the transverse component of nonlocal damping slows down the field-driven DW propagation and increases the Walker breakdown field whereas it is neglected in many previous works in literature. The experimentally measured DW mobility variation with the damping tuned by doping with heavy rare-earth elements that had discrepancy from micromagnetic simulation are now well understood with the nonlocal damping. Our results suggest that the nonlocal damping should be properly included as a prerequisite for quantitative studies of current-induced torques in noncollinear magnetization.Comment: 9 pages, 4 figure

Time reversal Aharonov-Casher effect in mesoscopic rings with Rashba spin-orbital interaction

The time reversal Aharonov-Casher (AC) interference effect in the mesoscopic ring structures, based on the experiment in Phys. Rev. Lett. \textbf{97}, 196803 (2006), is studied theoretically. The transmission curves are calculated from the scattering matrix formalism, and the time reversal AC interference frequency is singled out from the Fourier spectra in numerical simulations. This frequency is in good agreement with analytical result. It is also shown that in the absent of magnetic field, the Altshuler-Aronov-Spivak type (time reversal) AC interference retains under the influence of strong disorder, while the Aharonov-Bohm type AC interference is suppressed.Comment: 5 pages, 4 figures, accepted by Phys. Rev.

Strain accommodation through facet matching in La1.85_\text{1.85}Sr0.15_\text{0.15}CuO4_\text{4}/Nd1.85_\text{1.85}Ce0.15_\text{0.15}CuO4_\text{4} ramp-edge junctions

Scanning nano-focused X-ray diffraction (nXRD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are used to investigate the crystal structure of ramp-edge junctions between superconducting electron-doped Nd$_\text{1.85}$Ce$_\text{0.15}$CuO$_\text{4}$ and superconducting hole-doped La$_\text{1.85}$Sr$_\text{0.15}$CuO$_\text{4}$ thin films, the latter being the top layer. On the ramp, a new growth mode of La$_\text{1.85}$Sr$_\text{0.15}$CuO$_\text{4}$ with a 3.3 degree tilt of the c-axis is found. We explain the tilt by developing a strain accommodation model that relies on facet matching, dictated by the ramp angle, indicating that a coherent domain boundary is formed at the interface. The possible implications of this growth mode for the creation of artificial domains in morphotropic materials are discussed.Comment: 5 pages, 4 figures & 3 pages supplemental information with 2 figures. Copyright (2015) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APL Mat. 3, 086101 (2015) and may be found at http://dx.doi.org/10.1063/1.492779

From cyber-security deception to manipulation and gratification through gamification

Over the last two decades the field of cyber-security has experienced numerous changes associated with the evolution of other fields, such as networking, mobile communications, and recently the Internet of Things (IoT) [3]. Changes in mindsets have also been witnessed, a couple of years ago the cyber-security industry only blamed users for their mistakes often depicted as the number one reason behind security breaches. Nowadays, companies are empowering users, modifying their perception of being the weak link, into being the center-piece of the network design [4]. Users are by definition "in control" and therefore a cyber-security asset. Researchers have focused on the gamification of cyber- security elements, helping users to learn and understand the concepts of attacks and threats, allowing them to become the first line of defense to report anoma- lies [5]. However, over the past years numerous infrastructures have suffered from malicious intent, data breaches, and crypto-ransomeware, clearly showing the technical "know-how" of hackers and their ability to bypass any security in place, demonstrating that no infrastructure, software or device can be consid- ered secure. Researchers concentrated on the gamification, learning and teaching theory of cyber-security to end-users in numerous fields through various techniques and scenarios to raise cyber-situational awareness [2][1]. However, they overlooked the users’ ability to gather information on these attacks. In this paper, we argue that there is an endemic issue in the the understanding of hacking practices leading to vulnerable devices, software and architectures. We therefore propose a transparent gamification platform for hackers. The platform is designed with hacker user-interaction and deception in mind enabling researchers to gather data on the techniques and practices of hackers. To this end, we developed a fully extendable gamification architecture allowing researchers to deploy virtualised hosts on the internet. Each virtualised hosts contains a specific vulnerability (i.e. web application, software, etc). Each vulnerability is connected to a game engine, an interaction engine and a scoring engine

Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3 / SrRuO3 bilayers

Epitaxial La0.67Sr0.33MnO3 (LSMO)/ SrRuO3 (SRO) ferromagnetic bilayers have been grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition with atomic layer control. We observe a shift in the magnetic hysteresis loop of the LSMO layer in the same direction as the applied biasing field (positive exchange bias). The effect is not present above the Curie temperature of the SRO layer (), and its magnitude increases rapidly as the temperature is lowered below . The direction of the shift is consistent with an antiferromagnetic exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic SRO layer. We propose that atomic layer charge transfer modifies the electronic state at the interface, resulting in the observed antiferromagnetic interfacial exchange coupling.Comment: accepted to Applied Physics Letter

Low-temperature heat transport of Nd_2CuO_4: Roles of Nd magnons and spin-structure transitions

We report the magnetic-field dependence of thermal conductivity (\kappa) of an insulating cuprate Nd_2CuO_4 at very low temperatures down to 0.3 K. It is found that apart from the paramagnetic moments scattering on phonons, the Nd^{3+} magnons can act as either heat carriers or phonon scatterers, which strongly depends on the long-range antiferromagnetic transition and the field-induced transitions of spin structure. In particular, the Nd^{3+} magnons can effectively transport heat in the spin-flopped state of the Nd^{3+} sublattice. However, both the magnon transport and the magnetic scattering are quenched at very high fields. The spin re-orientations under the in-plane field can be conjectured from the detailed field dependence of \kappa.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.

In vitro expanded human CD4+CD25+ regulatory T cells suppress effector T cell proliferation.

Regulatory T cells (Tregs) have been shown to be critical in the balance between autoimmunity and tolerance and have been implicated in several human autoimmune diseases. However, the small number of Tregs in peripheral blood limits their therapeutic potential. Therefore, we developed a protocol that would allow for the expansion of Tregs while retaining their suppressive activity. We isolated CD4+CD25 hi cells from human peripheral blood and expanded them in vitro in the presence of anti-CD3 and anti-CD28 magnetic Xcyte Dynabeads and high concentrations of exogenous Interleukin (IL)-2. Tregs were effectively expanded up to 200-fold while maintaining surface expression of CD25 and other markers of Tregs: CD62L, HLA-DR, CCR6, and FOXP3. The expanded Tregs suppressed proliferation and cytokine secretion of responder PBMCs in co-cultures stimulated with anti-CD3 or alloantigen. Treg expansion is a critical first step before consideration of Tregs as a therapeutic intervention in patients with autoimmune or graft-versus-host disease