Structure parameters and magnetic properties of nanosized strontium hexaferrite prepared by the sol-gel combustion method

The phase composition, structure parameters, and main magnetic characteristics of SrFe12O19 hexaferrite prepared by the sol-gel combustion method in combination with subsequent annealing at the temperature of 850°C for 6 hours are investigated. From the study of the magnetization curves in the pulsed magnetic fields the value of saturation magnetization of synthesized material was determined. The value of the magnetocrystalline anisotropy field was determined from the survey of the ferromagnetic resonance

Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co

The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers. © Published under licence by IOP Publishing Ltd

Effect of heat treatment on the structural parameters and magnetic properties of copper ferrite nanopowders obtained by the sol-gel combustion

Phase composition, structure parameters and basic magnetic characteristics obtained by the sol-gel combustion nanopowders of ferrospinel CuFe2O4 are investigated. A comparison of the properties of synthesized materials: first sample - immediately after the combustion of the gel and second sample - after annealing at 1073 K for 4 hours are performed. Annealing leads to an increase in the concentration of the phase with tetragonal crystal structure. Particle sizes and the value of anisotropy field of this phase also increased

Study of the magnetic anisotropy of the multiphase samples of the ferrimagnets with hexagonal crystal structure by the method of ferromagnetic resonance

The influence of machining conditions in a planetary ball mill on the phase composition, structural and magnetic parameters of hexaferrite powders composition BaFe12O19 was investigated. The properties of powders vary greatly depending on the power density and the time of machining. Magnetocrystalline anisotropy of multiphase powders was studied by the method of ferromagnetic resonance. The effective field of magnetic anisotropy is reduced by more than two times, with decreasing particle size of ~ 67 nm to ~ 10 nm when the processing time equal to 10 minutes. The flow of mechanochemical reactions during grinding leads to the disintegration of the hexagonal crystal phase and the formation of the magnetite phase with a small value of the magnetocrystalline anisotropy field

Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio

Identifying global centers of unsustainable commercial harvesting of species

Overexploitation is one of the main threats to biodiversity, but the intensity of this threat varies geographically. We identified global concentrations, on land and at sea, of 4543 species threatened by unsustainable commercial harvesting. Regions under high-intensity threat (based on accessibility on land and on fishing catch at sea) cover 4.3% of the land and 6.1% of the seas and contain 82% of all species threatened by unsustainable harvesting and > 80% of the ranges of Critically Endangered species threatened by unsustainable harvesting. Currently, only 16% of these regions are covered by protected areas on land and just 6% at sea. Urgent actions are needed in these centers of unsustainable harvesting to ensure that use of species is sustainable and to prevent further species' extinctions.Peer reviewe

Influence of characteristics of epicardial adipose tissue and myocardial sympathetic innervation on the development of late recurrence of atrial fibrillation after radiofrequency ablation

Aim. To investigate the relationship between radiological characteristics of epicardial adipose tissue (EAT) and myocardial sympathetic activity, as well as to study their association with late recurrence of atrial fibrillation (AF) after radiofrequency ablation (RFA).Material and methods. This prospective study included 26 people with persistent and long-standing persistent AF scheduled for interventional AF treatment. Before the RFA procedure, all patients underwent cardiac 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy to assess the myocardial sympathetic innervation and contrast-enhanced cardiac multislice computed tomography to assess pulmonary vein anatomy, left atrial volume, and EAT volume. Clinical follow-up, including 12-lead electrocardiography (ECG) and 24-hour ECG monitoring, was carried out 3, 6 and 12 months after RFA.Results. After the end of follow-up, the patients were divided into two groups: with AF recurrence (group 1, n=8) and without AF recurrence (group 2, n=18). Multivariate logistic analysis found that only the 123I-MIBG washout rate (odds ratio, 1,0943; 95% confidence interval, 1,0138-1,1812) proved to be an independent predictor of late AF recurrence after RFA. ROC analysis revealed that a 123I-MIBG washout rate >21% with a sensitivity of 75% and a specificity of 83,3% (AUC=0,844; p<0,001) predicts late AF recurrence after RFA.Conclusion. Parameters of myocardial sympathetic activity, assessed by 123I-MIBG myocardial scintigraphy, are associated with late AF recurrence after RFA in patients with persistent and long-standing persistent AF. There were no reliable data confirming associations between myocardial sympathetic innervation and radiological EAT indicators, as well as the effect of the latter on the risk of AF recurrence after RFA

Modifying the surface of cerium oxide nanopowders produced by physical method

Cerium oxide nanoparticles present an interesting material for different industrial applications in biotechnology and medicine. The CeO2 nanopowder was produced by the method of pulsed electron evaporation of ceramic oxide targets with condensation of the vapors in a low pressure gas. The modification of nanoparticle surface was made with sodium citrate and N-phosphonomethylaminodiacetic acid. The stable aqueous suspensions of CeO2 nanoparticles could not be obtained in the work. This is probably due to the high hydrophobic properties of the nanoparticle surface. The cerium oxide nanoparticles with different stabilizers exhibit luminescence properties. © 2019 Author(s)

EXPERIMENTAL RESEARCHING MECHANICAL CHARACTERISTICS AND PLA PLASTIC APPLICABILITY AFTER ELECTRON BEAM RADIATION TREATMENT

In this work, we studied the effect of an electron beam on PLA plastic samples made on a 3D printer was carried out. The samples were irradiated at various doses from 3 to 15 kGy. The results obtained indicate an increase in the hardness and brittleness of PLA plastic com-pared to the control group