V. M. Cherepanov

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.

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.

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.

Mössbauer spectra of hematite and magnetite nanoparticles in polymer composites

It is experimentally demonstrated that the shape of Mossbauer spectra of polymer composites based on single-domain magnetic particles depends more on an inter-particle interaction than on superparamagnetic properties of a separate particle. The characteristic features of the spectra of such systems with strong inter-particle interactions are separated, such as an asymmetric shape of lines with sharp outer and smeared inward sides and presence of central anomalously splitted doublet. It is shown that the three-level relaxation model, which takes into account the precession and diffusion of magnetization of single-domain particles between two local energy minima and one absolute energy maximum, allows to describe all characteristic features of the spectra of such systems.

Phonon softening near superconducting transition temperatures in high-Tc ceramics

Abstract Anomalous behavior of the Mossbauer factor ƒ for iron and tin impurity atoms in the ceramic of the 1-2-3 composition, which indicates a phonon softening near Tc and Tt≈190 K, was found by Mossbauer spectroscopy.

Structural instability and thermal history effects in oxygen-reduced superconducting ceramic YBa2(Cu0.983Fe0.017)3O6.8

Abstract The temperature dependencies of the Mossbauer parameters for 57Fe-doped YBa2Cu3Oy (y ≈ 6.80, Tc ≈ 80 K) reveal anomalies near 90, 170, 230 and 280 K. These anomalies were confirmed with X-ray diffraction and heat capacity measurements using the same samples. The thermal history of the sample was found to influence the superconducting characteristics and the temperature behavior of the Mossbauer effect probability and linewidth. The results are discussed on the basis of the calculated low temperature phase diagram and possible ferro- and antiferroelectric phase transitions.

119Sn Mössbauer study of the 5f-electron behavior in U(In1−xSnx)3

Abstract The electronic and magnetic properties of the heavy fermion U(In 1− x Sn x ) 3 compound have been investigated using the 23.8 keV Mossbauer resonance of 119 Sn. The wide spatial distribution of the 5f electrons in the system was found to lead to a strong hybridization with electrons of tin atoms. The sensitivity of Mossbauer isomer shift for 119 Sn to the transition of uranium 5f electrons from localized to itinerant behavior was found experimentally. The analysis of the temperature-dependent Mossbauer lineshape proves the presence of spin fluctuations near the transition point. Temperature dependence of the spin relaxation rate has been estimated.

Phonon spectrum softening near temperatures of superconducting and structural transitions in HTSC ceramic “1-2-3”

Anomalous behavior of the Mössbauer factorf for iron and tin impurity atoms in the ceramic of the 1-2-3 composition indicates a phonon softening nearTc andTt≈190 K.