Evolution of the structural and magnetic properties of sputtered Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) thin films upon the increase of Tb content.

Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) ternary alloys have been obtained by cosputtering from Tb_33Fe_67 and Fe_72Ga_28 targets. In contrast with other Tb-Fe-Ga compounds that consist of just one structural phase, the diffraction pattern of the Tb_7Fe_73Ga_20 shows the presence of two different phases related to binary Tb -Fe and Fe-Ga alloys. This microstructure evolves as the Tb content is increased, and for a Tb of 11 at.% X-ray diffractometry only evidences the presence of a phase close to the TbFe_2. Although none of the studied samples show perpendicular magnetic anisotropy, there is a significant component of the magnetization perpendicular to the sample plane. The increase of the Tb content on the compounds from 7 at.% to 11 at.% enhances this component most probably due to the shift of the microstructure towards one similar to the TbFe_2

Tailoring the magnetic anisotropy and domain patterns of sputtered TbFeGa alloys

We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The layers were deposited from two targets with compositions TbFe2 and Fe3Ga, respectively. The structural and magnetic properties do not only depend on the composition but also on the growth conditions. Alloys with the same composition but deposited using a DC or a pulsed power source in the TbFe2 target exhibit a different magnetic anisotropy. The perpendicular magnetic anisotropy, the size and topology of domain patterns can be tailored by changing the evaporation parameters of TbFe2. The width of the stripe domain increases from 235 to 835 nm when using the DC source in the TbFe2. We correlate this effect with Tb enrichment of the TbxFe1−x phases present in the samples

The role of surface to bulk ratio on the development of magnetic anisotropy in high Ga content Fe100-xGax thin films

In this work we show the development of bulk in-plane magnetic anisotropy in high Ga-content (Ga = 28 at. %) Fe_(100-x)Ga_x thin films as the layer thickness increases. This result is in clear contrast with the generally reported decrease of this anisotropy with the film thickness. We propose the interrelation between the enhancement of the Ga-pair correlations and a collinear distortion of the bcc structure within the sample plane as the origin of the magnetic anisotropy. Our results have been obtained by employing a combination of long and local range structural probe techniques with bulk and surface magnetic characterization techniques. The key point shown in this work is that the in-plane structural anisotropy and hence, the magnetic anisotropy, are developed as the layer thickness increases. This fact strongly suggests that the surface to bulk free energy ratio plays a key role in the formation of ordered phases with a distorted bcc cell in Fe_(100-x)Ga_x films with x around 28 at. %. Our work also shows the arising of new phenomena in these high Ga content alloys due to the close correlation between structural and magnetic properties

Morphological, structural and magnetic evolution of sputtered Fe70Ga30 thin films upon annealing in oxygen atmosphere

We report on the evolution of uncapped Fe_(70)Ga_(30) layers deposited by sputtering and post-growth annealed in oxygen atmosphere in a temperature range from 500 °C to 800 °C. We have investigated the morphology, structure and magnetic properties of films with a thickness of 200 nm deposited on Mo buffer layers on glass substrates. X-ray diffractometry shows a decrease of the lattice parameter up to 600 °C whereas a further increase of the temperature up to 800 °C promotes the transformation to Fe_2O_3. We have observed by x-ray absorption fine structure the partial oxidation of Ga and the formation of Ga aggregates at 600 °C. These aggregates form Ga-rich bubbles that can be observed on the sample surface from which Ga evaporates leaving a Ga-poor layer that is later oxidized into Fe_2O_3. The thermal treatment on oxygen atmosphere has also a clear impact on the magnetic properties of the layers. The uniaxial in-plane magnetic anisotropy of the as-grown film evolves to magnetic isotropy when annealed at 600 °C probably due to the segregation and formation of Ga-rich areas. After Ga evaporates from the sample, Fe is fully oxidized and only a weak ferromagnetism related to Fe_2O_3 is detected

Straight motion of half-integer topological defects in thin Fe-N magnetic films with stripe domains

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The ultra-long GRB 220627A at z=3.08

GRB 220627A is a rare burst with two distinct gamma-ray emission episodes separated by almost 1000 s that triggered the Fermi Gamma-ray Burst Monitor twice. High-energy GeV emission was detected by the Fermi Large Area Telescope coincident with the first emission episode but not the second. The discovery of the optical afterglow with MeerLICHT led to MUSE observations which secured the burst redshift to z=3.08, making this the most distant ultra-long gamma-ray burst (GRB) detected to date. The progenitors of some ultra-long GRBs have been suggested in the literature to be different to those of normal long GRBs. Our aim is to determine whether the afterglow and host properties of GRB 220627A agree with this interpretation. We performed empirical and theoretical modelling of the afterglow data within the external forward shock framework, and determined the metallicity of the GRB environment through modelling the absorption lines in the MUSE spectrum. Our optical data show evidence for a jet break in the light curve at ~1.2 days, while our theoretical modelling shows a preference for a homogeneous circumburst medium. Our forward shock parameters are typical for the wider GRB population, and we find that the environment of the burst is characterised by a sub-solar metallicity. Our observations and modelling of GRB 220627A do not suggest that a different progenitor compared to the progenitor of normal long GRBs is required. We find that more observations of ultra-long GRBs are needed to determine if they form a separate population with distinct prompt and afterglow features, and possibly distinct progenitors.Comment: 17 pages, accepted for publication in A&

The Wide-field Spectroscopic Telescope (WST) Science White Paper

The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participat

SUPerfici & Ricoprimenti per la Meccanica Avanzata e la Nanomeccanica

Si propone la costituzione di un laboratorio regionale (Net-LAB SUP&RMAN) focalizzato sulle tematiche tecnologico-scientifiche delle superfici e delle modifiche superficiali, dei ricoprimenti e delle nanotecnologie meccaniche, in grado di produrre un avanzamento delle conoscenze che sia di grande impatto tecnologico sulla realtà produttiva emiliano-romagnola, in particolare in relazione alla possibilità di collocarsi strategicamente, in condizioni competitive, sul mercato globale. Si propone di operare attraverso il coordinamento delle attività di ricerca pubblica e privata attualmente presenti sul territorio, in coerenza con gli obiettivi del PRRIITT della Regione Emilia Romagna e per la realizzazione dei più generali obiettivi del Distretto Hi-Mech. La fattibilità della proposta poggia sulla presenza, sul territorio regionale, di istituzioni scientifiche che hanno raggiunto, nel settore delle superfici solide, dei ricoprimenti ed in generale della nanoscienza, livelli di eccellenza ampiamente riconosciuti a livello nazionale ed internazionale, e di una realtà industriale caratterizzata da una produzione di alta qualità e solida collocazione sui mercati anche internazionali, che esprime l’esigenza di accedere ad un patrimonio di conoscenze ritenute essenziali per il proprio sviluppo. Si intende operare attraverso tre principali azioni: i) la promozione di un significativo avanzamento e di una reale integrazione della ricerca di base e applicata, operando con modalità progettuale su obiettivi ben definiti, così da realizzare un significativo breakthrough nelle competenze; ii) la creazione di linguaggi e competenze trasversali tra gli attori della ricerca e tra questi e il mondo produttivo, che consenta un efficace azione di trasferimento tecnologico; iii) una acquisizione di strumentazione e di personale che consenta di affrontare tematiche innovative ad un livello di eccellenza nazionale ed internazionale

Magnetic properties of sputtered Tb-Fe-Ga ternary compounds

The investigation on materials systems with perpendicular magnetic anisotropy (PMA) receives a large interest because of their applications in magnetic storage or in spintronic devices. Tb-Fe alloys were investigated because of their pretty large out-of-plane anisotropy constant. Recently, there have appeared reports about the influence of small amounts of Tb (< 1 at.%) in the magnetostriction of Fe-Ga alloys [1-3]. In other group of studies, the interest is the magnetic anisotropy of Tb-Fe-Ga compounds with a much higher Tb content [4-6]. We have studied how to control the magnetic properties of 250 nm thick Tb-Fe-Ga layers. Samples were cosputtered from two targets (TbFe2 and Fe3Ga) on glass substrates capped with a Mo layer. Two series of samples have been obtained depending on the power source (DC or pulsed) used in each target. Regardless of the power source used in the targets, we have found PMA in the Tb10Fe77Ga13 layers and an in-plane magnetic anisotropy for the Tb9Fe75Ga16. The Tb10Fe76Ga14 alloy has a magnetic anisotropy that depends on the power source. There is a clear PMA when using the DC power source in the TbFe2 target, whereas it changes to a weak PMA when using it in the Fe3Ga target. We have also found rotatable magnetic anisotropy in some samples. This means that the orientation of the magnetic domains depends on the direction of a previous applied magnetic field. This behavior can be used as a method for the determination of frauds produced by magnetic fields in devices such as water meters or hard disks [7]. References [1] T. Ma et al, Appl. Phys. Lett. 106, 112401 (2015). [2] W. Wu et al, Appl. Phys. Lett. 103, 262403 (2013). [3] L. Jiang et al, Appl. Phys. Lett. 102, 222409 (2013). [4] R. Ranchal et al, J. Alloys Compnd. 582, 839 (2014). [5] R. Ranchal and V. Gutiérrez-Díez, Thin Solid Films, 534, 557 (2013). [6] R. Ranchal et al, J. Alloys Compnd. 667, 262 (2016). [7] R. Ranchal, S. Fin, and D. Bisero. Spanish Patent, P201500492

Rotation of stripe domains in a sputter deposited Tb-Fe-Ga thin film

The interest in Tb-Fe-Ga alloys, prepared by techniques compatible with technological processes, has been increasing in the last years, due to their high magnetostriction combined with their potential application in spintronic devices. In this letter, we report the domain configurations of a Tb10Fe76Ga14 thin film grown by co-sputtering deposition. The film exhibits a weak perpendicular magnetic anisotropy (PMA) and the presence of discontinuous stripe domains. The application of an external field in the film plane, perpendicular to the stripe direction, induces the rotation of the stripes and the alignment of their axis with the field. This property of the material has been observed in the range of applied fields 0–70 mT, above which PMA disappears and stripe annihilation occurs