Insights onto the magnetic coupling at hexaferrite-based hard/soft bilayer systems

IBERTRIVA 2019 X Iberian Conference on Tribology – IBERTRIB, XI Iberian Vacuum Conference - RIVA, Seville, Spain,June 26-28Magnets are used in a variety of applications, such as generators, magnetic recording media, components in RF and microwave devices. However, many of these magnets contain s rare earths, critical elements whose extraction is environmentally harmful and that present price volatility risks. Their replacement by cheaper and more environmentally friendly materials is therefore sought. In our case, we have focused on magnetically hard strontium hexaferrite (SrFe 12O19, SFO) as the base for alternative permanent magnets (Figure 1a). The atomic arrangement of this ferrite results in a high magnetocrystalline anisotropy and a coercive field, however, its magnetization is moderate (1). It is well known that the coupling between a magnetically hard and soft material improved magnetization while avoiding a high cost in coercitivity loss (2). However, results have been disappointing so far as structural and geometrical limitations make it extremely challenging to fabricate. In this work, we aim at further understanding the magnetic coupling at hard -soft interfaces involving ferrites, for which we have deposited soft iron and cobalt metals on top of SrFe12O19 thin films with controlled easy-axis of magnetization. SFO thin films have been obtained by RF magnetron sputtering at 260W followed by a subsequent annealing in air of 850ºC. Their structure and composition was characterized by Raman spectroscospy (Figure 1b), Mössbauer spectroscopy, X-ray photoemission spectroscopy and low-energy electron microscopy (LEEM). We have grown the magnetically soft layer by molecular-beam epitaxy and we have analyzed the resulting bilayer system through photoemission electron microscopy, LEEM and vibrating-sample magnetometry. References [1] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Progress in Materials Science 57 (2012), pp 1191¿1334. [2] Eric E. Fullerton, J. S. Jiang, M. Grimsditch, C. H. Sowers, and S. D. Bader, Exchange-spring behavior in epitaxial hard/soft magnetic bilayers, Phys. Rev. B 58 (1998) 1219

Strontium hexaferrite platelets: a comprehensive soft X-ray absorption and Mössbauer spectroscopy study

IBERMÖSS-2019, Bilbao, 30-31 may 2019. --https://www.ehu.eus/es/web/ibermossmeetingStrontium ferrite (SFO, SrFe12O19) is a ferrite employed for permanent magnets due to its high magnetocrystalline anisotropy. Since its discovery in the mid-20th century, this hexagonal ferrite has become an increasingly important material both commercially and technologically, finding a variety of uses and applications. Its structure can be considered a sequence of alternating spinel (S) and rocksalt (R) blocks. All the iron cations are in the Fe3+ oxidation state and it has a ferrimagnetic configuration with five different cationic environments for the iron (three octahedral sites, a tetraedrical site and a bipiramidal site)[1,2]. We have studied the properties of SrFe 12O19 in the shape of platelets, up to several micrometers in width, and tens of nanometers thick, synthesized by a hydrothermal method. We have characterized the structural and magnetic properties of these platelets by Mössbauer spectroscopy, x-ray transmission microscopy (TMX), transmission electron microscopy (TEM), x-ray diffraction (XRD), vibrating-sample magnetometry (VSM), x-ray absorption spectroscopy (XAS), x-ray circular magnetic dichroism (XMCD) and photoemission electron microscopy (PEEM). To the best of our knowledge this is the first time that the x-ray absorption spectra at the Fe L 2,3 edges of this material in its pure form have been reported. The Mössbauer results recorded from these platelets both in the electron detection and transmission modes have helped to understand the iron magnetic moments determined by XMCD (Fig.1). The experimental results have been complemented with multiplet calculations aimed at reproducing the observed XAS and XMCD spectra at the Fe L 2,3 absorption edge, and by density functional theory (DFT) calculations to reproduce the oxygen K- absorption edge. Finally the domain pattern measured in remanence is in good agreement with micromagnetic simulations [3]

Oral Anticoagulation and Risk of Symptomatic Hemorrhagic Transformation in Stroke Patients Treated With Mechanical Thrombectomy: Data From the Nordictus Registry

Introduction: We aimed to evaluate if prior oral anticoagulation (OAC) and its type determines a greater risk of symptomatic hemorrhagic transformation in patients with acute ischemic stroke (AIS) subjected to mechanical thrombectomy. Materials and Methods: Consecutive patients with AIS included in the prospective reperfusion registry NORDICTUS, a network of tertiary stroke centers in Northern Spain, from January 2017 to December 2019 were included. Prior use of oral anticoagulants, baseline variables, and international normalized ratio (INR) on admission were recorded. Symptomatic intracranial hemorrhage (sICH) was the primary outcome measure. Secondary outcome was the relation between INR and sICH, and we evaluated mortality and functional outcome at 3 months by modified Rankin scale. We compared patients with and without previous OAC and also considered the type of oral anticoagulants. Results: About 1.455 AIS patients were included, of whom 274 (19%) were on OAC, 193 (70%) on vitamin K antagonists (VKA), and 81 (30%) on direct oral anticoagulants (DOACs). Anticoagulated patients were older and had more comorbidities. Eighty-one (5.6%) developed sICH, which was more frequent in the VKA group, but not in DOAC group. OAC with VKA emerged as a predictor of sICH in a multivariate regression model (OR, 1.89 [95% CI, 1.01–3.51], p = 0.04) and was not related to INR level on admission. Prior VKA use was not associated with worse outcome in the multivariate regression model nor with mortality at 3 months. Conclusions: OAC with VKA, but not with DOACs, was an independent predictor of sICH after mechanical thrombectomy. This excess risk was associated neither with INR value by the time thrombectomy was performed, nor with a worse functional outcome or mortality at 3 months

Dyslipidemias and stroke prevention: recommendations of the Study Group of Cerebrovascular Diseases of the Spanish Society of Neurology

Objetivo: Actualizar las recomendaciones de la Sociedad Española de Neurología para la prevención del ictus, tanto primaria como secundaria, en pacientes con dislipidemia. Desarrollo: Se ha realizado una revisión sistemática en Pubmed evaluando los principales aspectos relacionados con el manejo de las dislipidemias en la prevención primaria y secundaria del ictus, elaborándose una serie de recomendaciones relacionadas con los mismos. Conclusiones: En prevención primaria se recomienda determinar el riesgo vascular del paciente con el fin de definir los objetivos de LDLc. En prevención secundaria tras un ictus de origen aterotrombótico se recomienda un objetivo de LDLc < 55 mg/dl, mientras que en ictus isquémicos de origen no aterotrombótico, dado que su relación con dislipidemias es incierta, se establecerán los objetivos en función del grupo de riesgo vascular de cada paciente. Tanto en prevención primaria como secundaria las estatinas son los fármacos de primera elección, pudiendo asociarse ezetimiba y/o inhibidores de PCSK9 en aquellos casos que no alcancen los objetivos terapéuticosObjective We present an update of the Spanish Society of Neurology's recommendations for prevention of both primary and secondary stroke in patients with dyslipidaemia. Development We performed a systematic review to evaluate the main aspects of the management of dyslipidaemias in primary and secondary stroke prevention and establish a series of recommendations. Conclusions In primary prevention, the patient's vascular risk should be determined in order to define target values for low-density lipoprotein cholesterol. In secondary prevention after an atherothrombotic stroke, a target value < 55 mg/dL is recommended; in non-atherothombotic ischaemic strokes, given the unclear relationship with dyslipidaemia, target value should be established according to the vascular risk group of each patient. In both primary and secondary prevention, statins are the drugs of first choice, and ezetimibe and/or PCSK9 inhibitors may be added in patients not achieving the target valu

Trombosis aguda de la arteria basilar

Resumen: La trombosis aguda de la arteria basilar (TAB) ha sido considerada una catástrofe neurológica. Únicamente alrededor de un 20% de los pacientes alcanza un buen pronóstico con tratamiento convencional. Es importante establecer una sospecha diagnóstica precoz para evitar un retraso en el inicio del tratamiento. La evaluación diagnóstica incluye confirmación de la oclusión basilar y estimación de la viabilidad del tejido isquémico, y puede realizarse con resonancia magnética multiparamétrica o con angiotomografía computarizada combinada con sus imágenes fuente. La recanalización arterial precoz determina la posibilidad de alcanzar un buen pronóstico; sin embargo, se desconoce cuál es el mejor tratamiento de la TAB. No se ha demostrado que la trombólisis intraarterial sea superior a la intravenosa, de modo que en ausencia de contraindicaciones debe iniciarse cuanto antes la trombólisis intravenosa, que puede ser el tratamiento principal si no se cuenta con acceso al neurointervencionismo. Recientemente se han notificado tasas excelentes de buen pronóstico (50% de independencia funcional) empleando estrategias escalonadas de combinación de varias modalidades terapéuticas (trombólisis intravenosa ultraprecoz seguida de trombectomía mecánica endovascular de rescate). Estos resultados representan una esperanza para pacientes y neurólogos y suponen un reclamo para continuar innovando e investigando en este campo. Abstract: Acute basilar artery thrombosis (ABT) has been largely considered a neurological catastrophe. With conventional treatment, only around 20% of patients achieve functional independence. An early presumptive diagnosis is essential to avoid treatment delay. Either multiparametric magnetic resonance imaging or computed tomography angiography source images may represent valid non-invasive tools to confirm ABT and evaluate ischemic tissue viability.The main determinant of ABT outcome is early recanalization but the most effective therapeutic option remains to be clarified. The BASICS prospective registry showed no superiority of intra-arterial over intravenous thrombolysis. Therefore, in the absence of contraindications, intravenous thrombolysis should be started as soon as possible and can be used as the main therapy when interventional procedures are not available. However, recent case series have reported high rates of functional independence (50%) after staged escalation therapy (ultra-early intravenous thrombolysis followed by on-demand endovascular mechanical thrombectomy). These results represent a hope for patients and neurologists and reinforce the need for innovation and research in this field. Palabras clave: Ictus, Pronóstico, Trombosis basilar, Cuidados neurocríticos, Keywords: Stroke, Outcome, Basilar thrombosis, Neurocritical car

Nanosecond infrared pulsed laser deposition of cobalt ferrite thin films on Si (100) substrates.

2018 E-MRS Spring Meeting. June 19 – 21, 0f 2018, at the Convention Centre of Strasbourg (France). .-https://www.european-mrs.com/meetings/2018-spring/exhibitionCobalt ferrite has attracted interest in various fields such as high-temperature superconductivity, spintronics, microelectronics and magnetic applications. Cobalt ferrite is a mixed iron (III) and cobalt (II) oxide with a spinel-related structure. Our work is focused on understanding the growth of cobalt ferrite thin films on Si (100) by pulsed laser deposition (PLD). The study is aimed at investigating the influence that deposition parameters such as substrate temperature, target-substrate distance or oxygen partial pressure have on the physicochemical properties of the obtained films and, in particular, in cation oxidation states, cation distribution and crystal quality

Mössbauer studies on nanosecond infrared pulsed laser deposition of cobalt ferrite thin films on Si(100) substrates

MECAME 2018.The Conference will take place from 27 to 31 May, 2018 at Kolovare Hotel, Zadar, Croatia.in honour of Professor Frank Berry (University of Birmingham, UK). .-https://mecame2018.irb.hr

Synthesis of smooth amorphous thin films of silicon carbide with controlled properties through pulsed laser deposition

10 pags., 5 figs., 1 tab.Thin films of silicon carbide (SiC) on Si (100) and SrTiO (100) substrates have been grown by nanosecond pulsed laser deposition (PLD) with a Q-switched Nd:YAG laser operating at the wavelengths of 1064, 532 and 266 nm. The deposits obtained consisted of smooth and uniform layers of amorphous SiC, free of holes and cracks, with thicknesses in the range of 30–100 nm and average roughness substantially lower than 1 nm. The role of laser wavelength and of substrate temperature (300 K vs. 1025 K) on morphology, crystallinity and composition of the deposits was assessed. The films were analyzed by X-ray diffraction, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. In addition, optical emission spectroscopy was employed to evaluate the characteristics of the ablation plasma and its correlation with the film growth.This research was supported by the Spanish State Research Agency (AEI) and European Regional Development (FEDER) through Projects PID2019-106125GB-I00/AEI/0.13039/501100011033 and PID2019-104124RB-I00/AEI/0.13039/501100011033. Thanks are given to the Soft and Polymeric Matter group (IEM-CSIC) for the use of AFM. We are grateful to M. Furió from MNCN-CSIC and P. Gonzalez from ICTP-CSIC for Raman and X-ray difraction technical assistance, respectively. Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature

Cu@Au self-assembled nanoparticles as SERS-active substrates for (bio)molecular sensing

9 pags. 6 figs.Cu0(core)-Au0(shell) (Cu@Au) bimetallic nanoparticles (NPs) synthesized under microwave-assisted heating were interrogated for surface enhanced Raman scattering (SERS)-active substrates. NPs characterization, by XRD, XPS and UV/vis spectroscopy, showed the formation of self-assembled particles with the occurrence of electron transfer from Cu to Au and the absence of CuxO. TEM and AF4 demonstrated NPs with a mean diameter of 4.7 nm. Despite the low LSPR shown by small nanoparticles (<10 nm diameter), our Cu@Au NPs showed enhanced SERS effect, demonstrated by the calculated scattering signal enhancement factor (3 × 105), which may be related to electromagnetic coupling. Selected examples of analytes of interest, including some biomolecules, were studied to demonstrate the versatility of our Cu@Au NPs as SERS-active substrates.Funded by Chief Scientists Office (TCS/16/07), Tenovus Scotland(G15-03) and the University of Aberdeen Development Trust. KCNgratefully acknowledges the University of Aberdeen for theElphinstone PhD scholarship (RG13451-10) and to Postnova Ana-lytics UK for the loan of the AF4 system together with training,support, and advice on the technique. AM Mendez gratefully ac-knowledges CONICYT (National Commission of Scientific andTechnological Research, Chile) for scholarship (21160174). Micro-scopy was performed in the Microscopy and Histology Core Facilityat the University of Aberdeen

Influence of the deposition parameters on the properties of silicon carbide thin films grown by PLD

IUMRS - ICAM International Conference on Advanced Materials, Symposium V: Laser interactions with materials: from fundamentals to applications, Nice, France (Congress & Exhibition Centre Acropolis), May 27 to 31, 2019. -- https://www.european-mrs.com/meetings/2019-spring-meetingSilicon carbide (SiC) has attracted much attention in the last years due to its excellent physical and electrical properties, such as wide bandgap, high thermal conductivity, high breakdown electric field, high saturated electron drift velocity and resistance to chemical attack. These properties make SiC a promising material for high-temperature, high-power and high-frequency electronic devices as well as for optoelectronic such as solar cells, image sensors, gas sensors and photodiodes, just to cite a few. Thin films of SiC on Si (100) and SrTiO3 (100) substrates were grown by nanosecond pulsed laser deposition (PLD) at the wavelengths of 1064, 532 and 266 nm using a Q-switched Nd:YAG laser. Upon irradiation for two hours at a repetition rate of 10 Hz and a distance target-substrate of 4 cm, deposits consisted of smooth and uniform layers, holes and cracks free, with average roughness ¿ 1 nm and with 20 to 100 nm thicknesses as determined by atomic force microscopy in tapping mode. The effect of laser irradiation wavelength, laser fluence and the temperature of the substrate (300 K vs. 1025 K) on the morphology, composition and crystallinity of the deposits was determined. Deposits were analyzed by X-ray diffraction, micro-Raman spectroscopy and X-ray photoelectron spectroscopy to characterize their crystallinity and composition. Additionally, the nanomechanical properties of the deposited films and the photoluminescence were evaluated