Vitalii Kapitan

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.

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.

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.

The magnetic states and Labyrinth ordering in 2D lattices of ising spins with RKKY Interaction

The numerical simulation of 2D simple square lattice of Ising superspins, that interact via the Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange interaction is performed. It is found, that at low temperatures in the researched systems predominantly realized labyrinth domain structure. The modeled image of magnetization distribution does not coincide with the image of energy distribution. Hysteresis loops of the samples and labyrinth domain structures similarly obtained by Monte Carlo method, are also observed in physical experiments.

High Performance Calculation of Magnetic Properties and Simulation of Nonequilibrium Phenomena in Nanofilms

Images of surface topography of ultrathin magnetic films have been used for Monte Carlo simulations in the frame of the ferromagnetic Ising model to study the hysteresis and thermal properties of nanomaterials. For high-performance calculations, a super-scalable parallel algorithm was used for finding the equilibrium configuration. The changing of the distribution of spins on the surface during the reversal of the magnetization and the dynamics of the nanodomain structure of thin magnetic films under the influence of a changing external magnetic field were investigated.

Magnetic Nanoparticles Arrays for Quantum Calculations

In frames of a quantum computer implementation, the ordered array of magnetic dipoles nanoparticles is considered. The phase space calculated for system of dipoles, which interact through long-range magnetostatic field. The behavior of nanoarchitectures in an external magnetic field is studied. The degeneracy of the equilibrium magnetic states depending on the value of an external magnetic field and the spin excess of configurations are determined. The presence of degeneration is a classical analog of quantum superposition, and distribution of probability of magnetic state is a classical representation of such quantum phenomena as entanglement.