The paper examines the impact of interparticle interactions on the superparamagnetic relaxation of ultrasmall nanoparticle ensembles, using Fe2O3∙nH2O iron oxyhydroxide (ferrihydrite) nanoparticles as an example. Two samples were analyzed: ferrihydrite of biogenic origin (with an average particle size of ⟨ d ⟩ ≈ 2.7 nm) with a natural organic shell, and a sample (with ⟨ d ⟩ ≈ 3.5 nm) that underwent low-temperature annealing, during which the organic shell was partially removed. The DC and AC magnetic susceptibilities (χ′(T), χ′′(T)) in a small magnetic field in the superparamagnetic (SPM) blocking region of the nanoparticles were measured. The results show that an increase in interparticle interactions leads to an increase in the SPM blocking temperature from 28 to 52 K according to DC magnetization data. It is shown that below the SPM blocking temperature, magnetic interactions of nanoparticles lead to the formation of a collective state similar to spin glass in bulk materials. The scaling approach reveals that the dynamics of correlated magnetic moments on the particle surface slow down with increasing interparticle interactions. Simulation of χ′′(T) dependence has shown that the dissipation of magnetic energy occurs in two stages. The first stage is directly related to the blocking of the magnetic moment of nanoparticles, while the second stage reflects the spin-glass behavior of surface spins and strongly depends on the strength of interparticle interactions.

By the example of α-Fe2O3 hematite, 5Fe2O3⋅9H2O ferrihydrite, and γ-Fe2O3 maghemite powders, a microwave-radiation-induced powder system temperature growth ΔTmax of several degrees has been measured in the ferromagnetic resonance mode at a frequency of 8.9 GHz. The powders heat up the most in the external field H coinciding with the ferromagnetic resonance field. The value of the ΔTmax effect depends on the magnetization of a powder material. The results obtained allow us to propose a new magnetic hyperthermia method for biomedical applications.

Ferrihydrite nanoparticles are synthesized and characterized. The dependences of heating of powders are studied upon pumping by a high-frequency electromagnetic field on a dc magnetic field. It is shown that the experimental dependence of the temperature of particles on a dc magnetic field is consistent with the theory of ferromagnetic resonance for an isotropic superparamagnet.

The magnetic-field dependence of the superparamagnetic-blocking temperature TB 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 TB(H), demonstrate peculiar features, indicating the influence of magnetic interparticle interactions. A detailed analysis of the dependences TB(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.

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.

Ferrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.

Ferrihydrite nanoparticles were synthesized using Klebsiella oxytoca microorganisms under various culti-vation conditions. The cultivation of bacteria was carried out under various lighting conditions, and the duration of cultivation varied from 3 to 56 days. Biogenic ferrihydrite nanoparticles were studied by Mossbauer spectroscopy, magnetometry, and small-angle X-ray scattering. The process of formation of ferrihydrite nanoparticles and the states arising during the cultivation of microorganisms have been investigated. The results of Mossbauer spectroscopy showed that, depending on the time of cultivation, three different states of ferrihydrite can be realized. States differ both in the ratio of defective and non -defective positions, and the size of the particle. Experimental results indicate that ferrihydrite nanopar-ticles are a system of variable composition and pass through several structural (or morphological) states during the cultivation of microorganisms. A model of the structure of ferrihydrite nanoparticles is pro-posed, which consists in the presence of an antiferromagnetic dense core with a high Neel temperature and a friable shell with a significantly lower temperature of magnetic ordering. CO 2022 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan All rights reserved.

The numbers of hydrocarbon-oxidizing and ammonifying microorganisms (psychrophilic and mesophilic) in the soils of the aeration zone and groundwater polluted with petroleum products under application of mineral fertilizers were analyzed. In the soils of the aeration zone, the numbers of aerobic microorganisms increased by 1-2 orders of magnitude, ammonifying ones - up to 10(7) CFU/g, hydrocarbon oxidizing microorganisms - up to 10(6) CFU/g. In groundwater the numbers of psychrophilic hydrocarbon-oxidizing microorganisms increased from 10(4) to 10(7) CFU/mL, mesophilic ones from 10(5) to 10(7) CFU/mL; the numbers of ammonifying microorganisms increased from 10(4) to 10(8) and from 10(5) to 10(7) CFU/mL, respectively. The number and variety of protozoa also increased. In the soils only flagellates of Bodo genus were found, their numbers during processing changed from 10-10(2) to 10(3) cells/g; in groundwater from 10(2)-10(3) to 10(4) cells/mL. The number of ciliata (Ciliata, Uronema genus) in groundwater changed from tens of cells per mL to 10(2)-10(3) cells/mL. After treatment, ciliata were detected in all water samples, and in addition to Uronema genus ciliata of Colpoda genus were discovered. The biostimulation produced changes in the chemical composition of groundwater (ammonium, nitrate concentration e.t al.), permanganate oxidizability of water, that indicated the decomposition of petroleum products and the appearance of easily oxidizable organic substances in water. The concentration of petroleum products in groundwater over the course of 3 years has decreased from 120-500 to 1.5-10.0 mg/dm(3).

Samples of synthetic ferrihydrite with an average nanoparticle size of 2.7 nm have been examined by magnetometry and Mossbauer spectroscopy. Ferrihydrite is characterized by the antiferromagnetic interactions between the magnetic moments of iron atoms. In ferrihydrite nanoparticles, as in any other anti ferromagnetic 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 Mossbauer 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 Mossbauer spectra at temperatures of the transition from the superparamagnetic to blocked state. The temperature dependence of the particle relaxation time obtained from the Mossbauer spectra points out the collective effect of freezing of the magnetic moments of particles due to the magnetic interactions between them. (c) 2021 Elsevier B.V. All rights reserved.

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 Mossbauer spectroscopy and magnetometry. Based on the Mossbauer 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 (K-v = 1.2.10(5) erg/cm(3) and K-s = 0.1 erg/cm(2)) is reached because of the highly developed ferrihydrite nanoparticles' surface. According to the Mossbauer 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 approximate to 2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.(C) 2020 Elsevier B.V. All rights reserved.

Changes in the number of anaerobic microorganisms (denitrifying, sulfate, and iron-reducing) in ground and groundwater polluted with oil products have been investigated during bioremediation. It is shown that, in the studied geological media, the number of psychrophilic microorganisms of anaerobic groups (denitrifying and sulfate and iron-reducing, as assessed by the number of the colony-forming units on the respective cultivation media) is higher than the number of mesophilic ones. When N, P, and K fertilizers are introduced into the contaminated zone, the number of psychrophilic microorganisms changes more significantly, both increasing and decreasing. When the ground in the aeration zone is treated, the number of anaerobes decreases, probably due to competitive displacement by aerobes. The number of hydrocarbon-oxidizing and ammonifying microorganisms increases by an order of magnitude to 106 CFU/g and 106–107 CFU/g, respectively. When fertilizers are added to groundwater, the number of anaerobic microorganisms increases 1-4 orders of magnitude and the number of denitrifiers reaches 105 CFU/mL, whereas the CFU number of sulfate and iron reducers is 103–104 and 102–103 CFU/mL, respectively. It is revealed that, simultaneously with the increase in CFU numbers, some chemical properties change, indicating the intensified biodegradation of petroleum products. In particular, antiphase changes in the ammonium and nitrate concentrations are observed due to the decomposition of petroleum products, nitrification, and denitrification, as well as the concentration of bicarbonate and sulfate ions due to sulfate reduction.

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.

In this work, we studied the relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles under the conditions of realization of the exchange bias effect for these systems. Magnetization relaxation is characterized by a logarithmic dependence on time, which is typical for thermo-activation processes of the hopping of the magnetic moment of particles through potential barriers caused by magnetic anisotropy. The energy of the barriers obtained from processing the data on relaxation of the remanent magnetization (under the conditions of field cooling) significantly exceeds that for ordinary conditions (zero field cooling). The observed difference indicates the possibility of using the residual magnetization relaxation process to analyze the mechanisms responsible for the effect of exchange bias in antiferromagnetic nanoparticles and obtain the parameters characterizing the exchange coupling of magnetic subsystems in such objects.

A sol containing biogenic ferrihydrite nanoparticles is obtained by cultivating Klebsiella oxytoca microorganisms. Data on the physical properties of the biogenic ferrihydrite and its effect on the organism of laboratory animals are obtained using a model of experimental hemolytic anemia, according to indicators of the functional activity of erythrocytes and morphological descriptions of organs.

The article presents the results of studying and evaluating the impact of magnetic nanoparticles of ferrihydrite on neutrophil granulocytes in human blood (in vitro) in order to determine their bio compatibility and eco toxicity. The subject soft here search were blood neutrophil granulocytes of 29 conditionally-healthy donors of blood, as well as magnetic nanoparticles of ferrihydrite (NP), the preparation dose in minimum concentration reached 25 mg, in maximum concentration it reached 50 mg per 106 cells/ml. We implemented the sol of magnetic NP, obtained by biogenic synthesis in International Scientific Centre for Studying Extreme States of an Organism. Functional activity of blood neutrophil granulocytes has been determined by luminol-dependent chemiluminescence. Magnetic NP were introduced into pilot samples straight before chemiluminescent analysis, and also after the incubation with in 30 minutes under 37 °С entigrade. As a result of thee stimation of the early response of neutrophil granulocytes to the influence of minimum concentration of magnetic NP in vitro we found statistically true decrease of the intensity (1.6 times), the area under the curve (2.1 times) in zymosan-induced chemiluminescent response, the activation index (2.3 times). When evaluating the late response of neutrophil granulocytes to the influence of maximum concentration of magnetic NP in vitro we have found statistically true lowering of the time of reaching the peak (10 times) of spontaneous chemiluminescence. More over we marked consider able lowering of maximum intensity 6 times and the reduction of the area under the curve of zymosan-induced chemiluminescence 5.6 times under the influence of magnetic NP under the lowering of activation index 3.7 times. The authors determined that magnetic NP were intensively decreasing the functional activity of neutrophil granulocytes. The intensity of the impact is higher under the preliminary incubation of the cells with magnetic NP. At the same time, short effect of magnetic NP to neutrophil granulocytes can be a modulating one and depends on the initial level of cell reactivity. We revealed that magnetic NP influence concerns only activated cells.

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.

Ferromagnetic resonance was used to study three types of ferrihydrite nanoparticles: nanoparticles formed as a result of the cultivation of microorganisms Klebsiella oxytoca; chemically prepared ferrihydrite nanoparticles; chemically prepared ferrihydrite nanoparticles doped with Cu. It is established from the ferromagnetic resonance data that the frequency-field dependence (in the temperature range ТP < T < T*) is described by the expression: 2πν/γ = НR + HA(T = 0)(1 – T/Т*), where γ is the gyromagnetic ratio, HR is the resonance field. The induced anisotropy HA is due to the spin-glass state of the near-surface regions. TP temperature characterizes the energy of the interparticle interaction of nanoparticles.

Ferrihydrite nanoparticles (2–3 nm in size), which are products of the vital activity of microorganisms, are studied by the ferromagnetic resonance method. The "core" of ferrihydrite particles is ordered antiferromagnetically, and the presence of defects leads to the appearance of an uncompensated magnetic moment in nanoparticles and the characteristic superparamagnetic behavior. It is established from the ferromagnetic resonance data that the field dependence of the frequency is described by the expression 2πν/γ = HR + H(=0)A(1 − T/T*), where γ is the gyromagnetic ratio, HR is the resonance field, HA ≈ 7 kOe, and T* ≈ 50 K. The induced anisotropy HA is due to the spin-glass state of the near-surface regions.