Konstantin V. Nefedev

Monte Carlo simulation of lattice systems with RKKY interaction

Numerical approaches to the study of the magnetic states, properties, and phase transitions in the Ising spin systems with the long-range exchange interaction is presented. The Monte Carlo calculations have been performed for a system of Ising spins on a square lattice with long-range RKKY interaction. It is shown that the Monte Carlo simulation systems RKKY interaction leads to the formation of a complex of the magnetic structure. We compared the results of simulation with experimental images of domain structure of garnet ferrite films.

Magnetic States of Nanoparticles with RKKY Interaction

Conditions of phase transitions in systems of identical ferromagnetic spherical nanoparticles randomly distributed in metal nonmagnetic matrix and superlattices of small number of nanoparticles with the Ruderman-Kittel-Kasuya-Yosida interaction are researched. In the framework of the Ising model the behavior of superspins is well described with the random interaction field method. The alteration of the effective magnetic moment due to the change in volume affects the choice of the magnetic state of the system: ferromagnetic spin glass or antiferromagnetic spin glass. The ground state of superlattice depends on the distance between particles.

Magnetic States of Nanodot Arrays. Physical and Numerical Experiments

The research method for the investigation of magnetic states of single nanoparticles, 1D arrays, 2D, and quasi-2D arrays is used. The possibility of the nanodots magnetic states reconstruction by the space distribution of gradient dipole-dipole interaction force is theoretically justified. The comparison is made between the results of nanoarchitecture numerical simulation in an external magnetic field and experimental data.

The Inverse Task for Magnetic Force Microscopy Data

The computer processing of cobalt nanodots magnetic force microscopy was fulfilled. The solution of reverse task of magnetic force microscopy is obtained for surface nanosystems. Superposition of fields, which are generated by a system of magnetic moments in the selected point in space, causes a linear dependence of the force gradient of the dipole-dipole interaction between the components of the vectors.

Concentration Phase Transition and Hysteresis Phenomena in Co-Nanofilms. Computer Data Processing and Simulation

The critical phenomena on cobalt monolayer films were studied by means of computersimulation. Proposed approach on the base of data of scanning tunneling microscopy gives possibilityestimate of critical concentration needed for concentration transition into ferromagnetic state. Assumptionabout presence of critical switching field allowed simulated hysteresis loops for given 1.5,2.0, 2.5 and 3.0 ML cobalt samples in frame of Ising model, which ones have qualitative agreementwith magnetometric data.

Magnetic Phase Transitions in the Lattice Ising Model

In this paper we consider an approach, which allows the research of order-disorder transitionin lattice systems (with any distribution of the exchange integrals) in the frame of Ising model. Anew order parameters, which can give a description of a phase transitions, are found. The commondefinition of such order parameter is the mean value of percolation cluster size. Percolation clusterincludes spins in ground state. The transition from absolute disorder to correlated phase could bestudied with using of percolation theory methods.

Specific Heat of Square Spin Ice in Finite Point Ising-Like Dipoles Model

In the model of finite number (up to 24) of point Ising-like magnetic dipoles with magnetostatic interaction on square 2D lattice within the framework of statistical physics, with using Gibbs formalism and by the means of Metropolis algorithm the heating dependence of temperature has been evaluated. The temperature dependence of the heat capacity on finite number of point dipoles has the finite value of maximum. Together with increase of the system in size the heating peak grows and moves to the area with higher temperature. The obtained results are useful in experimental verification of statistical models, as well as in development and testing of approximate calculation methods of systems with great number of particles.

Supercomputer data processing and simulation of MFM and STM experiments

For interpretation of experimental data obtained by the MFM were used two computational methods. These methods of simulation of macrospin distribution can be used for research of magnetization reversal processes of nanodots. The critical phenomena observed in cobalt monolayer films obtained by the STM were studied by computer simulation.

Spin-Glass-Like Behavior and Concentration Phase Transitions in Model of Monolayer Two-Sublattice Magnetics

Two-sublattice magnets with competing direct exchange interactions can exhibit spin-glass properties. It is shown that the Ising model on a 2D lattice with z = 8 nearest neighbors takes place divergence between the ZFC and FC magnetization curves. It was shown, that a weak antiferromagnetic interaction between ferromagnetically ordered sublattices with approximately similar values of the magnetic moments in the sites can lead to very complex magnetic properties. Theoretical magnetic phase diagram for the structures with random dilution was built.

Partition Function and Density of States in Models of a Finite Number of Ising Spins with Direct Exchange between the Minimum and Maximum Number of Nearest Neighbors

The results of studies of 1D Ising models and Curie-Weiss models partition functions structure are presented in this work. Exact calculation of the partition function using the authors combinatorial approach for such system is discussed. The distribution of the energy levels degeneracy was calculated. Analytical solution for density of states of 1D Ising chain were obtained. Generating functions for these models were obtained. It was suggested that in Curie-Weiss model the transition to a low-energy state occurs without the formation of separation boundaries