arXiv subjects

Andrey A. Kuznetsov

Publications and source records attributed to Andrey A. Kuznetsov.

7 recordsLinked to original sources

arXiv2026

Drift-diffusion interplay in active Brownian particles under orienting field

Magnetic active particles offer a versatile route to externally controlled microscale transport by combining self-propulsion with field-tunable orientation, as realized in both synthetic and living magnetic microswimmers. Here, we develop a theoretical framework for three-dimensional active Brownian motion in a uniform magnetic field, incorporating coupled translational and rotational dynamics and providing analytical approximations for low-order displacement moments. At long times, the system dynamics reduces to a combination of enhanced diffusion and permanent drift absent in regular active Brownian particles. The field acts as an external controller, channeling activity toward one of these two types of motion. At intermediate time scales, the interplay between rotational noise, self-propulsion, and magnetic alignment results in pronounced non-Gaussian displacement statistics. First-passage properties exhibit strong field sensitivity, highlighting the potential of magnetic guidance to optimize search processes and targeted delivery in active matter systems. Theoretical predictions are validated by numerical simulations.

cond-mat.soft↗

arXiv2025

Thermal Stoner-Wohlfarth Model for Magnetodynamics of Single Domain Nanoparticles: Implementation and Validation

We present the thermal Stoner-Wohlfarth (tSW) model and apply it in the context of Molecular Dynamics simulations. The model is validated against an ensemble of immobilized, randomly oriented uniaxial particles (solid superparamagnet) and a classical dilute ferrofluid for different combinations of anisotropy strength and magnetic field/moment coupling, at a fixed temperature. We compare analytical and simulation results to quantify the viability of the tSW model in reproducing the equilibrium (with and without dipole-dipole interactions) and dynamic (without dipole-dipole interactions) properties of magnetic soft matter systems. We show that if the anisotropy of a particle is more than five times higher than the thermal fluctuations, tSW is applicable and efficient. This approach allows one to consider the interplay between Néel and Brownian relaxation, often neglected in the fixed point-dipole representation-based magnetic soft matter theoretical investigations.

physics.comp-ph↗

arXiv2023

Magnetostatic response and field-controlled haloing in binary superparamagnetic mixtures

Nowadays, magnetoresponsive soft materials, based not simply on magnetic nanoparticles, but rather on multiple components with distinct sizes and magnetic properties, both in liquid and polymeric carriers, are becoming more and more wide-spread due to their unique and versatile macroscopic response to an applied magnetic field. The variability of the latter is related to a complex interplay of the magnetic interactions in a highly non-uniform internal fields caused by spatial inhomogeneity in multicomponent systems. In this work, we present a combine analytical and simulation study of binary superparamagnetic systems, containing nanoclusters and dispersed single-domain nanoparticles, both in liquid and solid carrier matrices. We investigate the equilibrium magnetic response of these systems in wide ranges of concentrations and interaction energies. It turns out that, while the magnetisation of a binary solid can be both above and below that of an ideal superparamagnetic gas, depending on the concentration of the dispersed phase and the interparticle interactions, the system in a liquid carrier is highly magnetically responsive. In liquid, a spatial redistribution of the initially homogeneously dispersed phase in the vicinity of the nanocluster is observed -- the effect that is reminiscent of the so-called ``haloing'' effect previously observed experimentally on micro- and milli-scales.

cond-mat.soft↗

arXiv2020

Interparticle Correlations in the Simple Cubic Lattice of Ferroparticles: Theory and Computer Simulations

Anisotropic interparticle correlations in the simple cubic lattice of single-domain ferroparticles (SCLF) are studied using both theory and computer simulation. The theory is based on the Helmholtz free energy expansion like classical virial series up to the second virial coefficient. The analytical formula for the Helmholtz free energy is incorporated in a logarithmic form to minimize the effects of series truncation. The new theoretical approach, including discrete summation over lattice nodes coordinates, is compared critically against the classical virial expansion of the Helmholtz free energy for the dipolar hard sphere fluid; the main differences between the Helmholtz free energy of SCLF and dipolar hard sphere fluid are discussed. The theoretical results for the Helmholtz free energy, the magnetization, and the initial magnetic susceptibility of the SCLF are compared against Molecular Dynamic simulation data. In all cases, theoretical predictions using logarithmic form of the Helmholtz free energy are seen to be superior, but they only have an applicability range of the effective dipolar coupling constant $λ_e < 1.5$. For highest values of $λ_e$, the structural transition of the magnetic dipoles in SCLF is observed in Molecular Dynamic simulation. It has been shown that for $λ_e \gtrsim 2$, an antiferromagnetic order appears in the system.

cond-mat.mtrl-sci↗

arXiv2018

Force acting on a cluster of magnetic nanoparticles in a gradient field: a Langevin dynamics study

Magnetophoretic force acting on a rigid spherical cluster of single-domain nanoparticles in a constant-gradient weak magnetic field is investigated numerically using the Langevin dynamics simulation method. Nanoparticles are randomly and uniformly distributed within the cluster volume. They interact with each other via long-range dipole-dipole interactions. Simulations reveal that if the total amount of particles in the cluster is kept constant, the force decreases with increasing nanoparticle concentration due to the demagnetizing field arising inside the cluster. Numerically obtained force values with great accuracy can be described by the modified mean-field theory, which was previously successfully used for the description of various dipolar media. Within this theory, a new expression is derived, which relates the magnetophoretic mobility of the cluster with the concentration of nanoparticles and their dipolar coupling parameter. The expression shows that if the number of particles in the cluster is fixed, the mobility is a nonmonotonic function of the concentration. The optimal concentration values that maximize the mobility for a given amount of magnetic phase and a given dipolar coupling parameter are determined.

cond-mat.mes-hall↗

arXiv2018

Equilibrium properties of magnetic filament suspensions

Langevin dynamics is used to study equilibrium properties of the suspension of magnetic filaments (chains of nanoparticles permanently crosslinked with polymers). It is shown that the filament suspension generally has a larger magnetic susceptibility than the system of unlinked nanoparticles with the same average particle concentration. However, actual susceptibility gain strongly depends on length and flexibility of filaments. It is also shown that in a strong gravitational (centrifugal) field sedimentation profiles of filaments are less homogeneous than that of unlinked particles. The spatial distribution of filaments weakly depends on the intensity of interparticle dipole-dipole interactions.

cond-mat.soft↗

arXiv2018

Equilibrium magnetization of a quasispherical cluster of single-domain particles

Equilibrium magnetization curve of a rigid finite-size spherical cluster of single-domain particles is investigated both numerically and analytically. The spatial distribution of particles within the cluster is random. Dipole-dipole interactions between particles are taken into account. The particles are monodisperse. It is shown, using the stochastic Landau-Lifshitz-Gilbert equation that the magnetization of such clusters is generally lower than predicted by the classical Langevin model. In a broad range of dipolar coupling parameters and particle volume fractions, the cluster magnetization in the weak field limit can be successfully described by the modified mean-field theory, which was originally proposed for the description of concentrated ferrofluids. In moderate and strong fields, the theory overestimates the cluster magnetization. However, predictions of the theory can be improved by adjusting the corresponding mean-field parameter. If magnetic anisotropy of particles is additionally taken into account and if the distribution of the particles' easy axes is random and uniform, then the cluster equilibrium response is even weaker. The decrease of the magnetization with increasing anisotropy constant is more pronounced at large applied fields. The phenomenological generalization of the modified mean-field theory, that correctly describes this effect for small coupling parameters, is proposed.

cond-mat.mes-hall↗