Ferromagnetic resonance spectra of linear magnetosome chains.

The ferromagnetic resonance (FMR) spectra of oriented and non-oriented assemblies of linear magnetosome chains are calculated by solving the stochastic Landau-Lifshitz equation. The dependence of the shape of the FMR spectrum of a dilute assembly of chains on the particle diameter, the number of particles in a chain, the distance between the centers of neighboring particles, the mutual orientation of the cubic axes of particle anisotropy, and the value of the magnetic damping constant is studied. It is shown that FMR spectra of non-oriented chain assemblies depend on the average particle diameter at a fixed thickness of the lipid magnetosome membrane, as well as on the value of the magnetic damping constant.

Specific absorption rate of randomly oriented magnetic nanoparticles in a static magnetic field.

Numerical simulations using the stochastic Landau-Lifshitz equation are performed to study magnetization dynamics of dilute assemblies of iron oxide nanoparticles exposed to an alternating (ac) magnetic field with an amplitude = 200 Oe and a frequency = 300 kHz and a static (dc) magnetic field in the range = 0-800 Oe. The specific absorption rate (SAR) of the assemblies is calculated depending on the angle between the directions of the ac and dc magnetic fields. For the case of an inhomogeneous dc magnetic field created by two opposite magnetic fluxes, the spatial distribution of the SAR in the vicinity of the field-free point is obtained for assemblies with different nanoparticle size distributions.

Deconvolution of ferromagnetic resonance spectrum of magnetic nanoparticle assembly using genetic algorithm.

The ferromagnetic resonance (FMR) spectra of dilute random assemblies of magnetite nanoparticles with cubic magnetic anisotropy and various aspect ratios are calculated using the stochastic Landau-Lifshitz equation at a finite temperature, T = 300 K, taking into account the thermal fluctuations of the particle magnetic moments. Particles of non-spherical shape in the first approximation are described as elongated spheroids with a given semiaxes ratio a/b, where a and b are the long and transverse semiaxes of a spheroid, respectively. A representative database of FMR spectra is created for assemblies of randomly oriented spheroidal magnetite nanoparticles with various transverse diameters D = 5-25 nm, moderate aspect ratios a/b = 1.

Towards optimal thermal distribution in magnetic hyperthermia.

A linear combination of spherically symmetric heat sources is shown to provide optimal stationary thermal distribution in magnetic hyperthermia. Furthermore, such spatial location of heat sources produces suitable temperature distribution in biological medium even for assemblies of magnetic nanoparticles with a moderate value of specific absorption rate (SAR), of the order of 100-150 W/g. We also demonstrate the advantage of using assemblies of spherical magnetic nanocapsules consisting of metallic iron nanoparticles covered with non magnetic shells of sufficient thickness in magnetic hyperthermia.

Heating ability of elongated magnetic nanoparticles.

Low-frequency hysteresis loops and specific absorption rate (SAR) of various assemblies of elongated spheroidal magnetite nanoparticles have been calculated for a range of particle semiaxis ratios / = 1.0-3.0.

Properties of assembly of superparamagnetic nanoparticles in viscous liquid.

Detailed calculations of the specific absorption rate (SAR) of a dilute assembly of iron oxide nanoparticles with effective uniaxial anisotropy dispersed in a liquid are performed depending on the particle diameters, the alternating (ac) magnetic field amplitude H and the liquid viscosity. For small and moderate H values with respect to particle anisotropy field H the SAR of the assembly as a function of the particle diameter passes through a characteristic maximum and then reaches a plateau, whereas for sufficiently large amplitudes, H ~ H, the SAR increases monotonically as a function of diameter. The realization of viscous and magnetic oscillation modes for particle unit magnetization vector and director for moderate and sufficiently large H values, respectively, explains this behavior.

Equilibrium properties of assembly of interacting superparamagnetic nanoparticles.

The stochastic Landau-Lifshitz equation is used to investigate the relaxation process and equilibrium magnetization of interacting assembly of superparamagnetic nanoparticles (SPMNPs) uniformly distributed in a nonmagnetic matrix. For weakly interacting assembly, the equilibrium magnetization is shown to deviate significantly from the Langevin law at moderate and large magnetic fields under the influence of their magnetic anisotropies. For dense assemblies with noticeable influence of the magneto-dipole interaction, a significant dependence of the initial susceptibility on the assembly density is revealed.

Application of Magnetosomes in Magnetic Hyperthermia.

Nanoparticles, specifically magnetosomes, synthesized in nature by magnetotactic bacteria, are very promising to be usedin magnetic hyperthermia in cancer treatment. In this work, using the solution of the stochastic Landau-Lifshitz equation, we calculate the specific absorption rate (SAR) in an alternating (AC) magnetic field of assemblies of magnetosome chains depending on the particle size , the distance between particles in a chain , and the angle of the applied magnetic field with respect to the chain axis. The dependence of SAR on the / ratio is shown to have a bell-shaped form with a pronounced maximum.

Multi-domain structures in spheroidal Co nanoparticles.

The structure of multi-domain micromagnetic states in hcp cobalt nanoparticles of spheroidal shape has been studied using numerical simulation in the range of diameters 20-200 nm. The single-domain diameters of the particles are determined depending on their aspect ratio. The complicated vortex structure of domain walls for two- and three-domain micromagnetic configurations is investigated.

Dynamics of superparamagnetic nanoparticles in viscous liquids in rotating magnetic fields.

The dynamics of magnetic nanoparticles in a viscous liquid in a rotating magnetic field has been studied by means of numerical simulations and analytical calculations. In the magneto-dynamics approximation three different modes of motion of the unit magnetization vector and particle director are distinguished depending on frequency and amplitude of the rotating magnetic field. The specific absorption rate of a dilute assembly of superparamagnetic nanoparticles in rotating magnetic field is calculated by solving the Landau-Lifshitz stochastic equation for the unit magnetization vector and the stochastic equation for the particle director.

Heating ability of magnetic nanoparticles with cubic and combined anisotropy.

The low frequency hysteresis loops and specific absorption rate (SAR) of assemblies of magnetite nanoparticles with cubic anisotropy are calculated in the diameter range of = 20-60 nm taking into account both thermal fluctuations of the particle magnetic moments and strong magneto-dipole interaction in assemblies of fractal-like clusters of nanoparticles. Similar calculations are also performed for assemblies of slightly elongated magnetite nanoparticles having combined magnetic anisotropy. A substantial dependence of the SAR on the nanoparticle diameter is obtained for all cases investigated.

Magnetic Vortices as Efficient Nano Heaters in Magnetic Nanoparticle Hyperthermia.

Magnetic vortices existing in soft magnetic nanoparticles with sizes larger than the single-domain diameter can be efficient nano-heaters in biomedical applications. Using micromagnetic numerical simulation we prove that in the optimal range of particle diameters the magnetization reversal of the vortices in spherical iron and magnetite nanoparticles is possible for moderate amplitudes of external alternating magnetic field, H < 100 Oe. In contrast to the case of superparamagnetic nanoparticles, for the vortex configuration the hysteresis loop area increases as a function of frequency.

Interaction Effects in Assembly of Magnetic Nanoparticles.

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau-Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters, the intensity of the magneto-dipole interaction is determined mainly by the cluster packing density η = N V/V , where N is the average number of the particles in the cluster, V is the nanoparticle volume, and V is the cluster volume.

[Optimization of methodology and extension of indications for beta therapy of neoplasms of the eyelids, conjunctiva and cornea].

The paper offers a theoretical foundation and results after clinical approbation of the method developed by the authors for beta therapy by enlarged single doses using, if necessary, a speeded-up fractionating and split courses of radiation. Beta therapy was used in 220 patients with tumors of the eye lids, conjunctiva and cornea, single doses of radiation, 40 Gr daily or each other day. By their morphologic type the tumors were mostly malignant epithelial and pigmented new-formations (sarcoma, melanoma).