M. A. Polikarpov

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.

Temperature relaxation of a superferromagnetic state in dispersed hematite

The shape sensitivity of a dispersed hematite Mossbauer spectrum to the way of particle packing is detected experimentally. This effect is shown to result from reversible particle transition from superparamagnetic to superferromagnetic state due to correlation bounds arising between magnetization vectors of neighboring particles.

Simulation of the current induced by 63Ni beta radiation

The current generated by radiation from a 63Ni layer of variable thickness is simulated with the actual spectrum of emitted electrons and with their distribution over the angles for Si and SiC taken into account. The dependences of the generation rate for nonequilibrium charge carriers on the depth are obtained for the cases of several Ni film thicknesses for both materials. The results are compared with the simulation results for a monoenergetic electron beam that is perpendicular to a semiconductor detector. It is shown that, for both Si and SiC, it is possible to choose an energy value of the electron beam in a SEM such that the ratio of the currents induced by the SEM beam and beta radiation from 63Ni is essentially independent of the diffusion length.

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.

Comparison of the efficiency of 63Ni beta-radiation detectors made from silicon and wide-gap semiconductors

The current induced by the radiation from a 63Ni film of variable thickness is simulated taking into account the real spectrum of emitted electrons and their angular distribution for GaN. The efficiency of β-radiation detectors made from Si and SiC is estimated based on the results obtained in this paper and previously. Using a scanning electron microscope the efficiency of β-radiation detectors made from Si and SiC under conditions corresponding to β radiation from a Ni film with a thickness of 3 μm and activity of 10 mCi/cm2 is analyzed. It is shown that the efficiency of real Si-based structures is virtually as good as the efficiency of SiC-based structures.

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.

Relaxation Mössbauer Spectroscopy of Iron Oxides Nanoparticles in Superferrimagnetic Regime

Film composites based on magnetite Fe3O4 nanoparticles in the polyvinyl alcohol (PVA) matrix and the dried ferrofluid ARA-250 (Chemicell GmbH, Germany) were studied at temperatures 78-300 K by Mössbauer spectroscopy and magnetic measurements in magnetic fields H < 5 kOe. The Mössbauer spectra taken in magnetic fields show essential restoration of the magnetic hyperfine structure characteristic for the nanoparticles. The experimental Mössbauer spectra have been analyzed within the recently developed three-level [ and multi-level [ relaxation models of magnetic dynamics in an ensemble of single-domain particles. These models take into account the precession and diffusion of particles uniform magnetization as well as the particles size distribution and interparticle interactions.

119Sn Mössbauer study of CexLa1−xNiSn

Abstract 119 Sn Mossbauer spectra of the Ce x La 1− x NiSn compounds with x = 0, 0.85 and 1 have been measured at 300 K and 5 K. Spectral analysis within hyperfine energy distribution and sharpening methods reveals relaxation broadening at 5 K for all the compounds, which indicates the presence of magnetic fluctuations at low temperatures. Relaxation broadening is the most pronounced in the spectrum of Ce 0.85 La 0.15 NiSn.

Separation of Contributions of the Magnetic Relaxation and Diffusion of Nanoparticles in Ferrofluids by Analyzing the Hyperfine Structure of Mössbauer Spectra

The theory and method for analysis of Mössbauer spectra of magnetic nanoparticles in a fluid have been developed by generalizing the model of the magnetic dynamics of a Néel ensemble of antiferromagnetic particles to the case of ferrimagnetic iron oxides. The resulting model describing the “superposition” of the magnetic dynamics and translational motion of nanoparticles in ferrofluids has been tested in application to the simultaneous analysis of Mössbauer spectra of “dry” magnetite nanoparticles and the same particles in glycerol.

Betavoltaic battery performance: Comparison of modeling and experiment

A verification of the Monte Carlo simulation software for the prediction of short circuit current value is carried out using the Ni-63 source with the activity of 2.7 mCi/cm2 and converters based on Si p-i-n diodes and SiC and GaN Schottky diodes. A comparison of experimentally measured and calculated short circuit current values confirms the validity of the proposed modeling method, with the difference in the measured and calculated short circuit current values not exceeding 25% and the error in the predicted output power values being below 30%. Effects of the protective layer formed on the Ni-63 radioactive film and of the passivating film on the semiconductor converters on the energy deposited inside the converters are estimated. The maximum attainable betavoltaic cell parameters are estimated.