204 research outputs found
Acceleration of Diffusional Jumps of Interstitial Fe with Increasing Ge Concentration in Si1 â x Ge x Alloys Observed by Mössbauer Spectroscopy
Radioactive 57Mn isotopes have been implanted into Si1 â x Ge x crystals (x †0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atom
Exploiting the close-to-Dirac point shift of Fermi level in Sb2Te3/Bi2Te3 topological insulator heterostructure for spin-charge conversion
Properly tuning the Fermi level position in topological insulators is of
vital importance to tailor their spin-polarized electronic transport and to
improve the efficiency of any functional device based on them. Here we report
the full in situ Metal Organic Chemical Vapor Deposition (MOCVD) and study of a
highly crystalline Bi2Te3/Sb2Te3 topological insulator heterostructure on top
of large area (4'') Si(111) substrates. The bottom Sb2Te3 layer serves as an
ideal seed layer for the growth of highly crystalline Bi2Te3 on top, also
inducing a remarkable shift of the Fermi level to place it very close to the
Dirac point, as visualized by angle-resolved photoemission spectroscopy. In
order to exploit such ideal topologically-protected surface states, we
fabricate the simple spin-charge converter Si(111)/Sb2Te3/Bi2Te3/Au/Co/Au and
spin-charge conversion (SCC) is probed by spin pumping ferromagnetic resonance.
A large SCC is measured at room temperature, which is interpreted within the
inverse Edelstein effect (IEE), thus resulting in a conversion efficiency
lambda_IEE of 0.44 nm. Our results demonstrate the successful tuning of the
surface Fermi level of Bi2Te3 when grown on top of Sb2Te3 with a full in situ
MOCVD process, which is highly interesting in view of its future technology
transfer.Comment: Main text: 19 pages, 6 figures. Supplementary information are also
included in the file with additional 4 page
All-Optical Generation and Time-Resolved Polarimetry of Magnetoacoustic Resonances via Transient Grating Spectroscopy
The generation and control of surface acoustic waves (SAWs) in a magnetic material are objects of an intense research effort focused on magnetoelastic properties, with fruitful ramifications in spin-wave -based quantum logic and magnonics. We implement a transient grating setup to optically generate SAWs also seeding coherent spin waves via magnetoelastic coupling in ferromagnetic media. In this work we report on SAW-driven ferromagnetic resonance (FMR) experiments performed on polycrystalline Ni thin films in combination with time-resolved Faraday polarimetry, which allows extraction of the value of the effective magnetization and of the Gilbert damping. The results are in full agreement with measurements on the very same samples from standard FMR. Higher-order effects due to parametric modulation of the magnetization dynamics, such as down-conversion, up-conversion, and frequency mixing, are observed, testifying the high sensitivity of this technique
Role of B diffusion in the interfacial Dzyaloshinskii-Moriya interaction in Ta / Coââ FeââBââ/MgO nanowires
We report on current-induced domain wall motion in Ta/Co20Fe60B20/MgO nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient D=+0.06mJ/m2. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta buffer layer during annealing, which was observed by chemical depth profiling measurements. The experimental results are compared to one-dimensional model simulations including the effects of pinning. This modeling allows us to reproduce the experimental outcomes and reliably extract a spin-Hall angle ΞSH=-0.11 for Ta in the nanowires, showing the importance of an analysis that goes beyond the model for perfect nanowires
The GAPS Programme at TNG. LIII. New insights on the peculiar XO-2 system
Planets in binary systems are a fascinating and yet poorly understood
phenomenon. Since there are only a few known large-separation systems in which
both components host planets, characterizing them is a key target for planetary
science. In this paper, we aim to carry out an exhaustive analysis of the
interesting XO-2 system, where one component appears to be a system with only
one planet, while the other has at least three planets. Over the last 9 years,
we have collected 39 spectra of XO-2N and 106 spectra of XO-2S with the High
Accuracy Radial velocity Planet Searcher for the Northern emisphere (HARPS-N)
in the framework of the Global Architecture of Planetary Systems project, from
which we derived precise radial velocity and activity indicator measurements.
Additional spectroscopic data from the High Resolution Echelle Spectrometer and
from the High Dispersion Spectrograph, and the older HARPS-N data presented in
previous papers, have also been used to increase the total time span. We also
used photometric data from TESS to search for potential transits that have not
been detected yet. For our analysis, we mainly used PyORBIT, an advanced Python
tool for the Bayesian analysis of RVs, activity indicators, and light curves.
We found evidence for an additional long-period planet around XO-2S and
characterized the activity cycle likely responsible for the long-term RV trend
noticed for XO-2N. The new candidate is an example of a Jovian analog with
M, au, and . We also analyzed the
stability and detection limits to get some hints about the possible presence of
additional planets. Our results show that the planetary system of XO-2S is at
least one order of magnitude more massive than that of XO-2N. The implications
of these findings for the interpretation of the previously known abundance
difference between components are also discussed
Orbital obliquity of the young planet TOI-5398 b and the evolutionary history of the system
Multi-planet systems exhibit remarkable architectural diversity. However, short-period giant planets are typically isolated. Compact systems like TOI-5398, with an outer close-orbit giant and an inner small-size planet, are rare among systems containing short-period giants. TOI-5398's unusual architecture coupled with its young age (650 +/- 150 Myr) make it a promising system for measuring the original obliquity between the orbital axis of the giant and the stellar spin axis in order to gain insight into its formation and orbital migration. We collected in-transit (plus suitable off-transit) observations of TOI-5398 b with HARPS-N at TNG on March 25, 2023, obtaining high-precision radial velocity time series that allowed us to measure the Rossiter-McLaughlin (RM) effect. By modelling the RM effect, we obtained a sky-projected obliquity of lambda = 3.0(-4.2)(+6.8) deg for TOI-5398 b, consistent with the planet being aligned. With knowledge of the stellar rotation period, we estimated the true 3D obliquity, finding psi = (13.2 +/- 8.2) deg. Based on theoretical considerations, the orientation we measure is unaffected by tidal effects, offering a direct diagnostic for understanding the formation path of this planetary system. The orbital characteristics of TOI-5398, with its compact architecture, eccentricity consistent with circular orbits, and hints of orbital alignment, appear more compatible with the disc-driven migration scenario. TOI-5398, with its relative youth (compared with similar compact systems) and exceptional suitability for transmission spectroscopy studies, presents an outstanding opportunity to establish a benchmark for exploring the disc-driven migration model
- âŠ