M. A. Chuev

On the shape of the gamma resonance spectra of slowly relaxing nanoparticles in a magnetic field

A nonstandard shape of the gamma resonance spectra of nanoparticles in the form of inverted five-step pedestal has been predicted, observed, and analytically described. This shape corresponds to the limit of high temperatures and slow relaxation of the homogeneous magnetization of single-domain particles with axial magnetic anisotropy. To describe the Mössbauer spectra of the ensemble of chaotically oriented nanoparticles in a magnetic field, a continual magnetic-dynamics model has been developed in the limit of slow relaxation. This model adequately describes the polarization effects observed in the experimental absorption spectra. The revealed features significantly expand the methodical capabilities of Mössbauer spectroscopy for the diagnostics of magnetic nanomaterials.

Biodegradation of Magnetic Nanoparticles in Mouse Liver From Combined Analysis of Mössbauer and Magnetization Data

The potential of Mössbauer spectroscopy to study the biodegradation process of magnetic nanoparticles in vivo was demonstrated. Magnetic nanoparticles in form of ferrofluid were administrated to mice. The Mössbauer study of the mice liver samples has shown that in addition to the sextet of lines related to the injected nanoparticles there appears an intense doublet of lines in the spectra with increasing times after the particles administration. Further analysis showed that the doublet consists of two components related to the formation of iron-containing proteins and superparamagnetic behavior of the injected nanoparticles. Using combined analysis of three Mössbauer spectra taken at different external conditions and magnetization curves measured for each sample these components were separated and the evolution with time of each component was characterized.

On the thermodynamics of antiferromagnetic nanoparticles by example of Mössbauer spectroscopy

A quantum-mechanical model has been developed for describing the thermodynamics of an ensemble of ideal antiferromagnetic nanoparticles in the approximation of slowly relaxing macrospins of magnetic sublattices. This model is the foundation for the further development of the general theory for the magnetic dynamics of antiferromagnetic and ferrimagnetic nanoparticles. Moreover, it already allows a qualitative description of the difference between the thermodynamic properties of nanoparticles of different magnetic natures, including quantum effects, which have been observed for almost fifty years in many experimental Mössbauer absorption spectra of 57Fe nuclei in antiferromagnetic nanoparticles.

Magnetic Nanoparticle Degradation in vivo Studied by Mössbauer Spectroscopy

Magnetic nanoparticles belong to the most promising nanosized objects for biomedical applications. However, little is known about clearance of magnetic nanoparticles from the organism. In this work superparamagnetic iron oxide particles fluidMAG‐ARA were injected into tail vein of mice at a dose of 17 mg per 20 g body weight. At various time intervals after the injection the mice were sacrificed and their organs collected. A Mossbauer study allowed to detect magnetic particles in the liver and spleen and showed the degradation of the particles with incorporation of exogenous iron into paramagnetic ferritin‐like iron species.

On the shape of gamma-resonance spectra of ferrimagnetic nanoparticles under conditions of metamagnetism

A four-level relaxation model in the two-sublattice approximation has been proposed and implemented for the description of the Mössbauer spectra of ferrimagnetic nanoparticles under conditions of metamagnetism. This model is a basis for the further development of the theory of magnetic dynamics of ferrimagnetic nanoparticles and allows the qualitative description of the size effects, which for nearly half a century were observed repeatedly in the experimental absorption spectra of 57Fe nuclei in ferrimagnetic nanoparticles.

Interpretation of the Mössbauer Spectra of the Magnetic Nanoparticles in Mouse Spleen

We have developed a stochastic model for description of relaxation effects in the system of homogeneously magnetized single‐domain particles and applied the model to the analysis of Mossbauer spectra of magnetic nanoparticles (Chemicell ARA) and mouse spleen after i.v. injection into animals. We estimate that the fraction of exogenous iron in nanoparticles in the mouse spleen 3 months after injection was 0.27±0.03. The spectra of the residual nanoparticles in the spleen had almost the same isomer shift but smaller mean hyperfine magnetic field values indicating decrease in the magnetic anisotropy energy (size) of the particles compared to the initial ones in the course of biodegradation. Concentration of ferritin‐like iron was about three‐fold higher than that in the spleen of untreated animals showing ferritin‐like forms in the mouse spleen.

Biodegradation of Magnetic Nanoparticles in Rat Brain Studied by Mössbauer Spectroscopy

Superparamagnetic particles of Fe3O4 in ferrofluid were injected transcranially in the ventricle of the rat brain. At three months after the injection the rat was sacrificed and the brain was investigated by Mössbauer spectroscopy and histological Perls Prussian blue method. Histological examination demonstrated increased concentration of blue areas in parenchyma and on the dura mater of the brain of experimental rat in comparison with the brain of control rat, indicating appearance in the brain of some undegradable compound of iron. Mössbauer spectra showed the presence in the ferrofluid of both Fe3O4 nanoparticles and an additional chemical compound which contains ferric iron in the high-spin state. Comparison of the Mössbauer spectra of the ferrofluid, of the brain before injection and of the brain three months after injection shows that the Fe3O4 nanoparticles were removed from the brain in three months. At the same time this additional chemical compound does not decompose and remains in the brain intact.

Nutations of magnetizations of sublattices and their role in the formation of Mössbauer spectra of antiferromagnetic nanoparticles

The continuum model of the magnetic dynamics of an ensemble of antiferromagnetic nanoparticles in the two-sublattice approximation has been generalized to the case of the exact solution of the equations of motion for magnetizations of sublattices. The nontrivial excitation spectrum of such particles in the form of four excitation branches corresponding to the normal modes of self-consistent precession of magnetizations of sublattices, as well as the continuous spectrum of nutations of magnetizations accompanying these modes, corresponds completely to quantum-mechanical calculations and makes it possible to give a phenomenological interpretation of macroscopic quantum effects earlier observed in many experimental Mössbauer absorption spectra.

On the mechanism of the temperature evolution of the symmetric magnetic hyperfine structure of Mössbauer spectra of magnetic nanoparticles to the quadrupole doublet of lines

The multilayer relaxation model of Mössbauer spectra of an ensemble of single-domain particles has been generalized to the case of the presence of the electric field gradient on nuclei with a chaotic orientation of its principal axes. The generalized model makes it possible to take into account the physical mechanisms of the formation of the hyperfine structure of the spectra in the real situation and to numerically describe the qualitative features of the temperature evolution of the spectra from symmetric magnetic sextet to the quadrupole doublet of lines, which is observed in most experimental spectra of 57Fe nuclei in magnetic nanoparticles.

An efficient method of analysis of the hyperfine structure of gamma-resonance spectra using the Voigt profile

Gammaresonance (Mossbauer) spectroscopy is one of the most informative methods of investigating the chemical composition and structural, magnetic, and thermodynamic properties of materials. The Mossbauer absorption spectra in most cases consist of a large number of lines corresponding to nonequiva� lent positions of the Mossbauer atom in a sample. The lines are formed due to the hyperfine interaction of the nucleus spin with internal electric and magnetic fields, the value of which is determined by the properties of the material under investigation. The problem of determining the material properties is reduced in the first approximation to finding the spectral density of states P(ω), which in the best way describes the exper� imental absorption spectrum I(ω), i.e., solving the integral equation of a reasonably general form