Ferrihydrite is a low-crystalline nanoscale matter. The uncompensated magnetic moment of the ferrihydrite caused by the antiferromagnetic ordering of the magnetic moments of iron atoms and leads to ...the magnetic properties very similar to those of ferro- and ferrimagnetic nanoparticles. In this study, we investigated the biogenic ferrihydrite nanoparticles with the narrow size distribution and an average diameter of ≈2 nm obtained by the bacteria life cycle. The features caused by the surface effects and the inhomogeneous structure of ferrihydrite have been examined in the temperature range of 4–300 K using Mössbauer spectroscopy and magnetometry. Based on the Mössbauer data, we identified the superparamagnetic blocking temperature at the temperature of 30 K for the largest ferryhidrite particles. We established that the exceptional magnetic anisotropy of ferrihydrite (KV=1.2⋅105 erg/cm3 and KS=0.1 erg/cm2) is reached because of the highly developed ferrihydrite nanoparticles’ surface. According to the Mössbauer data, we propose a core-shell structural model of the biogenic ferrihydrite particles. We found that the size of the dense core depends on the particle size. The well-crystallized core is formed only for nanoparticles larger than ≈2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.
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•We discuss the core-shell structure of the biogenic ferrihydrite nanoparticles using Mössbauer spectroscopy and magnetometry in the temperature range of 4–300 K.•We found that the size of the dense core depends on the nanoparticle size. The particles less than ≈2 nm have no dense core.•It was shown that the surface magnetic anisotropy originates from the inhomogeneous structure of the ferrihydrite particles
•Synthetic and biogenic ferrihydrite nanoparticles are synthesized.•Analysis of the Mössbauer spectra and magnetometry revealed the interparticle magnetic interactions in synthetic ...ferrihydrite.•Collective processes of freezing the magnetic moments of particles take place in synthetic ferrihydrite.
Samples of synthetic ferrihydrite with an average nanoparticle size of 2.7 nm have been examined by magnetometry and Mössbauer spectroscopy. Ferrihydrite is characterized by the antiferromagnetic interactions between the magnetic moments of iron atoms. In ferrihydrite nanoparticles, as in any other antiferromagnetic ones, structural defects induce the formation of an uncompensated magnetic moment, which determines the magnetic properties typical of single-domain ferro- and ferrimagnetic particles. The manifestation of the magnetic interactions between ferrihydrite nanoparticles in the magnetic properties of the material and in the temperature evolution of Mössbauer spectra has been in focus. The results obtained on synthetic ferrihydrite have been compared with the data for the biogenic ferrihydrite sample with a similar average size of particles surrounded by a polysaccharide shell, which weakens and screens the interparticle magnetic interactions. A clear manifestation of the effect of the interparticle magnetic interactions on the transition to the blocked state is the presence of a significant contribution of the relaxation component in the Mössbauer spectra at temperatures of the transition from the superparamagnetic to blocked state. The temperature dependence of the particle relaxation time obtained from the Mössbauer spectra points out the collective effect of freezing of the magnetic moments of particles due to the magnetic interactions between them.
We studied the effect of biogenic ferrihydrite nanoparticles synthesized as a result of the culturing of
Klebsiella oxytoca
on Wistar rats with experimental toxic hemolytic anemia. The pathology was ...simulated by single intraperitoneal injection of phenylhydrazine hydrochloride. On day 4, the functional parameters of erythrocytes in rats corresponded to the state of toxic hemolytic anemia. It is shown that ferrihydrite nanoparticles suspension has chronic toxicity and causes morphological changes in organs (mainly in the spleen), which are characterized by accumulation of nanoparticles. Administration of phenylhydrazine induced systemic vascular damage and the formation of extramedullary hematopoietic foci, which indicated a compensatory activation in hematopoiesis in the liver and spleen. Injection of nanoparticles reduced discirculatory and necrotic changes in the kidneys.
Using minor hysteresis loops in the Stoner–Wohlfarth model allows describing the experimental behavior of the coercive force of minor hysteresis loops in ferrihydrite nanoparticles with a change in ...the field amplitude. The description allows estimating the parameters of the distribution of the magnetic anisotropy field in nanoparticles. The best agreement of the anisotropy fields estimated by different approaches is achieved for the assumption of uniaxial anisotropy in ferrihydrite nanoparticles.
The relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles at the exchange bias effect implemented in these systems has been investigated. The ...magnetization relaxation depends logarithmically on time, which is typical of the thermally activated hoppings of particle magnetic moments through the potential barriers caused by the magnetic anisotropy. The barrier energy obtained by processing of the remanent magnetization relaxation data under the field cooling conditions significantly exceeds the barrier energy under standard (zero field cooling) conditions. The observed difference points out the possibility of using the remanent magnetization relaxation to analyze the mechanisms responsible for the exchange bias effect in antiferromagnetic nanoparticles and measure the parameters of the exchange coupling of magnetic subsystems in such objects.
The magnetic-field dependence of the superparamagnetic-blocking temperature
T
B
of systems of antiferromagnetically ordered ferrihydrite nanoparticles has been investigated and analyzed. We studied ...two powder systems of nanoparticles: particles of “biogenic” ferrihydrite (with an average size of 2.7 nm), released as a result of vital functions of bacteria and coated with a thin organic shell, and particles of biogenic ferrihydrite subjected to low-temperature annealing, which cause an increase in the average particle size (to 3.8 nm) and burning out of the organic shell. The character of the temperature dependences of magnetization, measured after cooling in a weak field, as well as the shape of the obtained dependences
T
B
(
H
), demonstrate peculiar features, indicating the influence of magnetic interparticle interactions. A detailed analysis of the dependences
T
B
(
H
) within the random magnetic anisotropy model made it possible to estimate quantitatively the intensity of magnetic particle–particle interactions and determine the magnetic anisotropy constants of individual ferrihydrite particles.
A regular monodisperse flow of spherical microtargets of solid hydrogen or deuterium with a variable diameter of several tens of micrometers and a frequency from several tens to several hundreds of ...kilohertz is in demand as internal targets in physical experiments at accelerators. The paper is devoted to the modification and launching of a prototype cryogenic corpuscular hydrogen target in which the gas entering the facility is transformed into a flow of spherical microtargets. Processes of cryogenic cooling and liquefaction of the gas, formation of a liquid microjet, and its controlled monodisperse disintegration into equal-sized drops are realized in the target, and they are followed by freezing of the drops and formation of microtargets upon injection into vacuum. The target prototype is composed of the cryogenic, vacuum, and gas systems as well as the systems for control and optical diagnostics of microtarget parameters. The modified target prototype provided monodisperse regimes of generation of microtargets with a diameter of 20–50 μm at a generation frequency of 260–465 kHz.
Confident effect of five magnetic composite nanoparticles (FeP@Ag, FeP@Pd, CoP, NiP, Fe2O3@AГ) on growth of test bacteria colonies (Acinetobacter baumannii, Еscherichia coli, Klebsiella pneumoniae, ...Pseudomonas aeruginosa, Staphylococcus aureus) in five replicates each is considered. Reliable inhibitors of colonies of all five test bacteria were nanoparticles FeP@Ag. CoP nanoparticles are reliable inhibitors of growth of 4 test bacteria (except for test bacteria Escherichia сoli). NiP nanoparticles are reliable inhibitors of growth of 2 test bacteria: Escherichia сoli and Klebsiella pneumoniae. Bacteria Escherichia сoli were most sensitive to the effect of magnetic nanoparticles; and bacteria Pseudomonas aeruginosa and Staphylococcus aureus were most resistant to the effect of magnetic nanoparticles. The prospects of the method are in the possibility of multiple reuse of the magnetic particles with antimicrobial properties for bacterial decontamination of the studied sources of water and removal of magnetic nanoparticles from the treated liquids by electromagnet. The method can find use in water treatment facilities for household, Industrial and medical wastes.
We studied the effectiveness of using magnetic ferrihydrite nanoparticles of bacterial origin carrying ampicillin for local treatment of burn wounds in rats using a magnetic field. It was found that ...the use of these nanoparticles in combination with a magnetic field accelerated wound healing and reduced the titer of microorganisms in comparison with the corresponding parameters in the untreated animals and animals treated with nanoparticles or ampicillin alone.
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