Magnon diffusion lengths in bulk and thin film Fe3O4 for spin Seebeck applications

The magnon diffusion length (MDL) is understood to play a major role in the thickness dependence of spin Seebeck effect (SSE) voltages in Fe3O4/Pt thin films. Here we extract the MDL in an Fe3O4 single crystal using inelastic neutron scattering (INS) and in Fe3O4/Pt thin films using accurate heat flux SSE and static magnetization measurements. The INS MDLs were 34 ± 8 nm at 300 K and 27 ± 6 nm at 50 K. The SSE MDLs decreased with temperature (19 ± 2 nm at 300 K and 13 ± 4 nm at 50 K), but were markedly smaller. Whilst the bulk MDL is expected to be an upper limit of the MDL in thin films, we show that the film magnetization must be considered to obtain MDLs from SSE measurements. This study highlights the importance of disentangling the role of various effects in SSE measurements which is crucial in increasing the efficiencies of thermomagnetic energy harvesting devices

Gaia Early Data Release 3: Gaia photometric science alerts

Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, CE = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is CI = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-Transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-Transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge. © S. T. Hodgkin et al. 2021

MEIS studies of oxygen plasma cleaning of copper for fast response time photocathodes used in accelerator applications

The performance of a fourth generation light source is to a greater extent reliant on the properties of the electron bunches, with the fundamental limit controlled by the photocathode where the electrons are emitted. Normally conducting RF guns often use metal photocathodes, mainly due to their fast response time that allows very short pulses to be generated. However, they typically have very low quantum efficiency (QE) compared to semiconductor alternatives (GaAs or Cs2Te). The drive to use higher QE metals is motivated by the need to minimize the laser power required to generate sufficient bunch charge for the downstream accelerator. The use of Cu as the metal photocathode of choice is long standing. However, the preparation of an atomically clean surface is thought to be key to achieving a high enough QE to be used in an RF gun. At STFC Daresbury laboratory a preparation procedure has been developed that has allowed a QE of approximately 10-5 to be achieved. This coupled with a high power UV laser system has allowed electron bunches of up to 250 pC to be generated in the Versatile Electron Linear Accelerator (VELA) facility [1]. However, there is very little understanding of how the cleaning procedure leads to the required surface properties for electron emission and hence a detailed study has been initiated

Ultra-thin films and surface alloying of Pd on Cu(1 1 1) investigated by medium energy ion scattering

The structure of Pd films on Cu(1 1 1) and the alloying between the films and the substrate have been investigated by medium energy ion scattering (MEIS) using 100 keV H+ ions. Data are presented for the and alignments (nominal one- and three-layer alignments, respectively). It is found that beyond 1 ML the Pd grows in a twinned fcc structure, the incommensurate nature of which increases the visibility of the Cu(1 1 1) substrate to MEIS. Deposition of 0.2 ML of Pd produces a structure in which Pd mostly occupies the top two layers which have interlayer distances d12 = 208 4 pm and d23 = 211 4 pm. Some twinning is also present in this structure. Upon annealing 1.6 ML of Pd to 600 K for 1 min, the copper and palladium interdiffuse leaving around 0.4 ML of visible palladium. Energy plots show that there are several layers with an altered structure present over at least part of the surface. This may be due to large scale interdiffusion or alloy island formation. Incremental annealing to successively higher temperatures shows that the structural transformation begins around 500 K

The structure formed by the deposition of a sub-monolayer quantity of platinum onto Cu(110) investigated using medium energy ion scattering

The structure of 0.35 monolayers of platinum deposited onto Cu(110) has been investigated using medium energy ion scattering. Quantitative analysis of the data has been performed using the VEGAS routine. It was found that platinum atoms mostly occupy the second layer with a first interlayer distance of d12 = 123 ± 4 pm and a separation of first and third layers of d13= 142− 10+ 4 pm. These represent a contraction of 4% and an expansion of 11% respectively from the ideal termination of the Cu(110) surface. There is clear evidence of the presence of some platinum in the third layer

Investigation of the structure of ultra-thin films of Fe on Cu(111) using medium-energy ion scattering

Investigation of the structure of ultra-thin films of Fe on Cu(111) using medium-energy ion scatterin

Influence of ion assisted deposition on interface broadening in Fe/Al multilayers investigated by medium energy ion scattering

Trilayers of Al/Fe/Al and Al/Fe multilayers produced by magnetron sputtering both with and without ion assistance have been depth profiled using Auger electron spectroscopy and medium energy ion scattering. Important differences are observed in the layer structure, with ion assisted deposition giving the narrowest Al/Fe interfaces and so maintaining the most clearly defined layer structure. Both types of sputtering result in some oxygen contamination, particularly at the surface that modeling shows to be associated with the Al layers

Application of the ‘Climafor’ Approach to Estimate Baseline Carbon Emissions of a Forest Conservation Project in the Selva Lacandona, Chiapas, Mexico

baselines, carbon emissions, deforestation, forest conservation, Mexico, risk matrices,