A Numerical Model of Crossed Andreev Reflection and Charge Imbalance

We present a numerical model of local and nonlocal transport properties in a lateral spin valve structure consisting of two magnetic electrodes in contact with a third perpendicular superconducting electrode. By considering the transport paths for a single electron incident at the local F/S interface - in terms of probabilities of crossed or local Andreev reflection, elastic cotunneling or quasiparticle transport - we show that this leads to nonlocal charge imbalance. We compare this model with experimental data from an aluminum-permalloy (Al/Py) lateral spin valve geometry device and demonstrate the effectiveness of this simple approach in replicating experimental behavior.Comment: 9 pages, 14 figure

Magnetic microscopy of topologically protected homochiral domain walls in an ultrathin perpendicularly magnetized Co film

Next-generation concepts for solid-state memory devices are based on current-driven domain wall propagation, where the wall velocity governs the device performance. It has been shown that the domain wall velocity and the direction of travel is controlled by the nature of the wall and its chirality. This chirality is attributed to effects emerging from the lack of inversion symmetry at the interface between a ferromagnet and a heavy metal, leading to an interfacial Dzyaloshinskii-Moriya interaction that can control the shape and chirality of the magnetic domain wall. Here we present direct imaging of domain walls in Pt/Co/AlO$_x$ films using Lorentz transmission electron microscopy, demonstrating the presence of homochiral, and thus topologically protected, N\'{e}el walls. Such domain walls are good candidates for dense data storage, bringing the bit size down close to the limit of the domain wall width

The Aquaculture knowledge economy: boom or bust?

We live in an age of unprecedented growth in knowledge generation and exchange. The links between knowledge, innovation and economic development are frequently promoted. Government policies for enhancing education and training opportunities in a widening framework of Lifelong Learning are becoming increasingly central themes in strategies for economic recovery and growth. However, there is little evidence that more of the same i.e. traditionally structured education and training, is leading to the innovation and growth that policymakers desire. Graduate unemployment rates in Europe are reaching new highs and when new graduates are employed, it is often in lower skilled jobs than would have been the case in the past. In many ways it looks to be an economy of abundance; a massive increase in the availability of explicit knowledge gradually devaluing the people seeking employment on the basis of their accredited knowledge and skills. However, other interpretations are possible, not least that society generally, and large organisations and institutions in particular, are failing to grasp the opportunities that knowledge generation and exploitation can bring. The aquaculture sector is truly global and highly diverse; in parts relying on traditional tacit knowledge and elsewhere on the most recently generated explicit knowledge. A broader understanding of the role of different types of knowledge for aquaculture enterprise, and a deeper understanding of how that knowledge is generated, shared and communicated can provide a platform for dialogue and potentially new initiatives. Pointers for the future can also be found in new knowledge generating and sharing activities that are emerging on the Internet, and in different models of enterprise organisation found in innovative start-up companies. One interpretation is that lifelong and lifewide learning are the norm and that the tendency for compartmentalisation and institutionalisation of knowledge and learning may be constraining the benefits that individual, group and social learning can bring. The evidence for this is explored, and consideration given to how the aquaculture sector can unlock greater potential from its human capital. Reference is made to case studies, current initiatives and new collaborative platforms within the sector.info:eu-repo/semantics/publishedVersio

Limits of magnetic interactions in Ni-Nb ferromagnet-superconductor bilayers

Studies of ferromagnet-superconductor hybrid systems have uncovered magnetic interactions between the competing electronic orderings. The Electromagnetic Proximity Effect predicts the formation of a spontaneous vector potential inside a superconductor placed in proximity to a ferromagnet. In this work, we use a Nb superconducting layer and Ni ferromagnetic layer to test for such magnetic interactions. We use the complementary, but independent, techniques of polarised neutron reflectometry and detection Josephson junctions to probe the magnetic response inside the superconducting layer at close to zero applied field. In this condition, Meissner screening is negligible, so our measurements examine only additional magnetic and screening contributions from proximity effects. We report that any signals attributable to such proximity effects are below the detection resolution of our experimental study. We estimate a limit of the size of the zero field Electromagnetic Proximity Effect in our Ni-Nb samples to be $\pm$0.27 mT from our measurements.Comment: Main text 18 pages, 4 figures, 1 table. Plus SI 8 pages, 6 figure

High resolution magnetic microscopy based on semi-encapsulated graphene Hall sensors

The realization of quantitative, noninvasive sensors for ambient magnetic imaging with high spatial and magnetic field resolution remains a major challenge. To address this, we have developed a relatively simple process to fabricate semi-encapsulated graphene/hBN Hall sensors assembled by dry transfer onto pre-patterned gold contacts. 1 lm-sized Hall cross sensors at a drive current of 0.5 lA exhibit excellent room temperature sensitivity, SI 700 V/AT, and good minimum detectable fields, Bmin ¼ 0.54 G/Hz0.5 at a measurement frequency of 1 kHz, with considerable scope for further optimization of these parameters. We illustrate their application in an imaging study of labyrinth magnetic domains in a ferrimagnetic yttrium iron garnet film

Meissner screening as a probe for inverse superconductor-ferromagnet proximity effects

Funding: We acknowledge the support of the EPSRC through Grants No. EP/I031014/1, No. EP/J01060X, No. EP/J010634/1, No. EP/L015110/1, No. EP/R031924/1, and No. EP/R023522/1. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 743791 (SUPERSPIN). R.S. acknowledges funding under ETH Zurich Postdoctoral Fellowship 20-1FEL-36.We present experimental results on the observed flux screening in proximity coupled superconductor-ferromagnet thin film structures using Nb and Co as the superconductor and ferromagnet respectively. Using the low-energy muon-spin rotation technique to locally probe the magnetic flux density, we find that the addition of the ferromagnet (F) increases the total flux screening inside the superconductor. Two contributions can be distinguished. One is consistent with the predicted spin-polarization (or magnetic proximity) effect, while the other is in line with the recently emerged electromagnetic (EM) proximity models. Furthermore, we show that the addition of a few nanometers of a normal metallic layer between the Nb and the Co fully destroys the contribution due to electromagnetic proximity. This is unanticipated by the current theory models in which the magnetization in the F layer is assumed to be the only driving force for the EM effect and suggests the role of additional factors. Further experiments to explore the influence of the direction of the F magnetization also reveal deviations from theory. These findings are an important step forward in improving the theoretical description and understanding of proximity coupled systems.Publisher PDFPeer reviewe