Hardening of cobalt ferrite nanoparticles by local crystal strain release: implications for rare earth free magnets

In this work, we demonstrate that the reduction of the local internal stress by a low-temperature solvent-mediated thermal treatment is an effective post-treatment tool for magnetic hardening of chemically synthesized nanoparticles. As a case study, we used nonstoichiometric cobalt ferrite particles of an average size of 32(8) nm synthesized by thermal decomposition, which were further subjected to solvent-mediated annealing at variable temperatures between 150 and 320 °C in an inert atmosphere. The postsynthesis treatment produces a 50% increase of the coercive field, without affecting neither the remanence ratio nor the spontaneous magnetization. As a consequence, the energy product and the magnetic energy storage capability, key features for applications as permanent magnets and magnetic hyperthermia, can be increased by ca. 70%. A deep structural, morphological, chemical, and magnetic characterization reveals that the mechanism governing the coercive field improvement is the reduction of the concomitant internal stresses induced by the low-temperature annealing postsynthesis treatment. Furthermore, we show that the medium where the mild annealing process occurs is essential to control the final properties of the nanoparticles because the classical annealing procedure (T > 350 °C) performed on a dried powder does not allow the release of the lattice stress, leading to the reduction of the initial coercive field. The strategy here proposed, therefore, constitutes a method to improve the magnetic properties of nanoparticles, which can be particularly appealing for those materials, as is the case of cobalt ferrite, currently investigated as building blocks for the development of rare-earth free permanent magnets.This work was supported by EU-H2020 AMPHIBIAN Project (Grant no. 720853). A.L.O. acknowledges support from the Universidad Pública de Navarra (Grant no. PJUPNA2020). Open access funding provided by Universidad Pública de Navarra

Remanence plots as a probe of spin disorder in magnetic nanoparticles

Remanence magnetization plots (e.g., Henkel or δM plots) have been extensively used as a straightforward way to determine the presence and intensity of dipolar and exchange interactions in assemblies of magnetic nanoparticles or single domain grains. Their evaluation is particularly important in functional materials whose performance is strongly affected by the intensity of interparticle interactions, such as patterned recording media and nanostructured permanent magnets, as well as in applications such as hyperthermia and magnetic resonance imaging. Here, we demonstrate that δM plots may be misleading when the nanoparticles do not have a homogeneous internal magnetic configuration. Substantial dips in the M plots of γ-FeO nanoparticles isolated by thick SiO shells indicate the presence of demagnetizing interactions, usually identified as dipolar interactions. Our results, however, demonstrate that it is the inhomogeneous spin structure of the nanoparticles, as most clearly evidenced by Mössbauer measurements, that has a pronounced effect on the δM plots, leading to features remarkably similar to those produced by dipolar interactions. X-ray diffraction results combined with magnetic characterization indicate that this inhomogeneity is due to the presence of surface structural (and spin) disorder. Monte Carlo simulations unambiguously corroborate the critical role of the internal magnetic structure in the δM plots. Our findings constitute a cautionary tale on the widespread use of remanence plots to assess interparticle interactions as well as offer new perspectives in the use of Henkel and δM plots to quantify the rather elusive inhomogeneous magnetization states in nanoparticles

Global age-sex-specific mortality, life expectancy, and population estimates in 204 countries and territories and 811 subnational locations, 1950–2021, and the impact of the COVID-19 pandemic: a comprehensive demographic analysis for the Global Burden of Disease Study 2021

Background: Estimates of demographic metrics are crucial to assess levels and trends of population health outcomes. The profound impact of the COVID-19 pandemic on populations worldwide has underscored the need for timely estimates to understand this unprecedented event within the context of long-term population health trends. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 provides new demographic estimates for 204 countries and territories and 811 additional subnational locations from 1950 to 2021, with a particular emphasis on changes in mortality and life expectancy that occurred during the 2020–21 COVID-19 pandemic period. Methods: 22 223 data sources from vital registration, sample registration, surveys, censuses, and other sources were used to estimate mortality, with a subset of these sources used exclusively to estimate excess mortality due to the COVID-19 pandemic. 2026 data sources were used for population estimation. Additional sources were used to estimate migration; the effects of the HIV epidemic; and demographic discontinuities due to conflicts, famines, natural disasters, and pandemics, which are used as inputs for estimating mortality and population. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate under-5 mortality rates, which synthesised 30 763 location-years of vital registration and sample registration data, 1365 surveys and censuses, and 80 other sources. ST-GPR was also used to estimate adult mortality (between ages 15 and 59 years) based on information from 31 642 location-years of vital registration and sample registration data, 355 surveys and censuses, and 24 other sources. Estimates of child and adult mortality rates were then used to generate life tables with a relational model life table system. For countries with large HIV epidemics, life tables were adjusted using independent estimates of HIV-specific mortality generated via an epidemiological analysis of HIV prevalence surveys, antenatal clinic serosurveillance, and other data sources. Excess mortality due to the COVID-19 pandemic in 2020 and 2021 was determined by subtracting observed all-cause mortality (adjusted for late registration and mortality anomalies) from the mortality expected in the absence of the pandemic. Expected mortality was calculated based on historical trends using an ensemble of models. In location-years where all-cause mortality data were unavailable, we estimated excess mortality rates using a regression model with covariates pertaining to the pandemic. Population size was computed using a Bayesian hierarchical cohort component model. Life expectancy was calculated using age-specific mortality rates and standard demographic methods. Uncertainty intervals (UIs) were calculated for every metric using the 25th and 975th ordered values from a 1000-draw posterior distribution. Findings: Global all-cause mortality followed two distinct patterns over the study period: age-standardised mortality rates declined between 1950 and 2019 (a 62·8% [95% UI 60·5–65·1] decline), and increased during the COVID-19 pandemic period (2020–21; 5·1% [0·9–9·6] increase). In contrast with the overall reverse in mortality trends during the pandemic period, child mortality continued to decline, with 4·66 million (3·98–5·50) global deaths in children younger than 5 years in 2021 compared with 5·21 million (4·50–6·01) in 2019. An estimated 131 million (126–137) people died globally from all causes in 2020 and 2021 combined, of which 15·9 million (14·7–17·2) were due to the COVID-19 pandemic (measured by excess mortality, which includes deaths directly due to SARS-CoV-2 infection and those indirectly due to other social, economic, or behavioural changes associated with the pandemic). Excess mortality rates exceeded 150 deaths per 100 000 population during at least one year of the pandemic in 80 countries and territories, whereas 20 nations had a negative excess mortality rate in 2020 or 2021, indicating that all-cause mortality in these countries was lower during the pandemic than expected based on historical trends. Between 1950 and 2021, global life expectancy at birth increased by 22·7 years (20·8–24·8), from 49·0 years (46·7–51·3) to 71·7 years (70·9–72·5). Global life expectancy at birth declined by 1·6 years (1·0–2·2) between 2019 and 2021, reversing historical trends. An increase in life expectancy was only observed in 32 (15·7%) of 204 countries and territories between 2019 and 2021. The global population reached 7·89 billion (7·67–8·13) people in 2021, by which time 56 of 204 countries and territories had peaked and subsequently populations have declined. The largest proportion of population growth between 2020 and 2021 was in sub-Saharan Africa (39·5% [28·4–52·7]) and south Asia (26·3% [9·0–44·7]). From 2000 to 2021, the ratio of the population aged 65 years and older to the population aged younger than 15 years increased in 188 (92·2%) of 204 nations. Interpretation: Global adult mortality rates markedly increased during the COVID-19 pandemic in 2020 and 2021, reversing past decreasing trends, while child mortality rates continued to decline, albeit more slowly than in earlier years. Although COVID-19 had a substantial impact on many demographic indicators during the first 2 years of the pandemic, overall global health progress over the 72 years evaluated has been profound, with considerable improvements in mortality and life expectancy. Additionally, we observed a deceleration of global population growth since 2017, despite steady or increasing growth in lower-income countries, combined with a continued global shift of population age structures towards older ages. These demographic changes will likely present future challenges to health systems, economies, and societies. The comprehensive demographic estimates reported here will enable researchers, policy makers, health practitioners, and other key stakeholders to better understand and address the profound changes that have occurred in the global health landscape following the first 2 years of the COVID-19 pandemic, and longer-term trends beyond the pandemic

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Nouveaux états du Si dans les multicouches Co/Si

Nous avons étudié les propriétés structurales et physiques des multicouches Co/Si déposées par pulvérisation cathodique à 90 K dans le but de limiter la diffusion aux interfaces. Nous avons obtenu des multicouches très bien cristallisées quoique polycristallines, formées de très grands grains > 300 nm et un mélange limité par rapport à celui des multicouches déposées à 300 K. Cela nous a permis d'observer des phénomènes physiques nouveaux, originaux et spectaculaires dans ces multicouches : (1) Oscillation du couplage d'échange magnétique en accord avec les calculs ab initio, (2) Oscillation de la résistance de faible à forte et (3) Oscillation de la rugosité de l'interface, en fonction de l'épaisseur de Si. La période des ces oscillations, bien corrélées entre elles, est courte de l'ordre de 0.4 nm soit 2 ML. Cela nous a conduit de proposer une interprétation commune de ces résultats, basé sur le passage périodique au niveau de Fermi d'un état de puits quantique dans la couche de Si.In this work we studied the structural and physical properties of the Co/Si multilayers deposited by sputtering at 90 K with the aim of limiting the interdiffusion at interfaces. We have obtained very well crystallized multilayers although polycristalline, formed of very big grains > 300 nm with limited interfacial mixing as compared to that of multilayers deposited at 300 K. It allowed us to observe new, original and spectacular physical phenomena in these multilayers: (1) Oscillation of the interlayer exchange coupling in agreement with ab-initio calculations, (2) Oscillation of the multilayer resistance from weak to strong and (3) Oscillation of the roughness of the interface, according to the thickness of Si. The period of these oscillations, which are well correlated between them, is short of the order of 0.4 nm (2 ML). This led to us to propose a common interpretation of these results, based on the periodic passage at the Fermi level of a quantum well state in the Si layer

Nouveaux états du Si dans les multicouches Co/Si

Nous avons étudié les propriétés structurales et physiques des multicouches Co/Si déposées par pulvérisation cathodique à 90 K dans le but de limiter la diffusion aux interfaces. Nous avons obtenu des multicouches très bien cristallisées quoique polycristIn this work we studied the structural and physical properties of the Co/Si multilayers deposited by sputtering at 90 K with the aim of limiting the interdiffusion at interfaces. We have obtained very well crystallized multilayers although polycristallin

Nouveaux états du Si dans les multicouches Co/Si

Nous avons étudié les propriétés structurales et physiques des multicouches Co/Si déposées par pulvérisation cathodique à 90 K dans le but de limiter la diffusion aux interfaces. Nous avons obtenu des multicouches très bien cristallisées quoique polycristallines, formées de très grands grains > 300 nm et un mélange limité par rapport à celui des multicouches déposées à 300 K. Cela nous a permis d observer des phénomènes physiques nouveaux, originaux et spectaculaires dans ces multicouches : (1) Oscillation du couplage d échange magnétique en accord avec les calculs ab initio, (2) Oscillation de la résistance de faible à forte et (3) Oscillation de la rugosité de l interface, en fonction de l épaisseur de Si. La période des ces oscillations, bien corrélées entre elles, est courte de l ordre de 0.4 nm soit 2 ML. Cela nous a conduit de proposer une interprétation commune de ces résultats, basé sur le passage périodique au niveau de Fermi d un état de puits quantique dans la couche de Si.In this work we studied the structural and physical properties of the Co/Si multilayers deposited by sputtering at 90 K with the aim of limiting the interdiffusion at interfaces. We have obtained very well crystallized multilayers although polycristalline, formed of very big grains > 300 nm with limited interfacial mixing as compared to that of multilayers deposited at 300 K. It allowed us to observe new, original and spectacular physical phenomena in these multilayers: (1) Oscillation of the interlayer exchange coupling in agreement with ab-initio calculations, (2) Oscillation of the multilayer resistance from weak to strong and (3) Oscillation of the roughness of the interface, according to the thickness of Si. The period of these oscillations, which are well correlated between them, is short of the order of 0.4 nm (2 ML). This led to us to propose a common interpretation of these results, based on the periodic passage at the Fermi level of a quantum well state in the Si layer.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Modeling of magnetic and optical properties of nanoparticles in medical interest

Cette thèse porte sur la modélisation ab initio des ligands et des nanoparticules magnétiques utilisés en médecine (hyperthermie magnétique, imagerie médicale ...). Les calculs sont effectués par le logiciel Quantum Espresso base sur théorie de la fonctionnelle de la densité et LDA + U. L'objectif est d'abord de comprendre la liaison des ligands sur des nanoparticules magnétiques, la nature de l'ionicité dans les particules, puis de décrire le changement d'anisotropie magnétique due aux liaisons chimiques sur la surface, et enfin de décrire la modification des propriétés optiques due également à la liaison de différents ligands sur la surface de nanoparticules hybrides d'or et d'oxyde de fer.This thesis concerns the ab initio modeling of ligands and magnetic nanoparticles used in medicine (magnetic hyperthermia, medical imaging). Calculations are performed by the Quantum Espresso software based on density functional theory and LDA+U. The goal is first to understand the binding of ligands on magnetic nanoparticles, the nature of ionicity in the particles, then to describe the change in magnetic anisotropy due to the chemical bondings on surface, and finally to describe the change in optical properties due also to the bonding of various ligands or clusters on the surface of hybrid gold and iron oxide nanoparticles.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

Chemical Inhomogeneity in Iron Oxide@CoO Core–Shell Nanoparticles: A Local Probe Study Using Zero-Field and In-Field 57 Fe Mössbauer Spectrometry

International audienc