arXiv subjects

A. V. Zarubin

Publications and source records attributed to A. V. Zarubin.

16 recordsLinked to original sources

arXiv2026

The formation of magnetic reentrancy in the Ising model on a decorated square lattice

In our work, based on an exact solution of the Ising model on a decorated square lattice with an arbitrary number of decorating spins, we have demonstrated the fundamental possibility of describing the phenomenon of multiple magnetic phase transitions (magnetic reentrancy) in the regime of competing exchange interactions. We analyzed the magnetic behavior of the system and established the conditions for the occurrence of magnetic reentrancy. We have determined the relationships of the model parameter under which the formation of one, three, and even five magnetic phase transitions is possible, which is confirmed by a complicated magnetic phase diagram. We have also proposed a unique method for finding critical temperatures that allows for the precise determination of their number and values, including those at extremely low temperatures.

cond-mat.stat-mech↗

arXiv2024

Frustrations on Decorated Square Lattice in Ising Model

In this paper, we performed the comprehensive studies of frustration properties in the Ising model on a decorated square lattice in the framework of an exact analytical approach based on the Kramers--Wannier transfer matrix method. The assigned challenge consisted in finding rigorous formulas for residual entropies of all possible frustrations without exception and elucidating the influence of frustrations on the behavior of the thermodynamic functions of the system under discussion. The accomplished results turned out to be very rich and intricate, especially in comparison with the original undecorated square lattice, in which frustration properties are completely absent. Such an abundance of properties is due to the multiparametric problem of decorated lattice with four exchange interactions $J_{x}$, $J_{y}$, $J_{dx}$ and $J_{dy}$ taking on arbitrary continuous values and different signs: positive (ferromagnetic) and negative (antiferromagnetic), as well as with two discrete variables $d_{x}$ and $d_{y}$ (multiplicities of decorating spins in both lattice directions), corresponding to infinite natural series of numbers.

cond-mat.stat-mech↗

arXiv2023

Frustrations on decorated triangular lattice in Ising model

We study the frustration properties of the Ising model on a decorated triangular lattice with an arbitrary number of decorating spins on all lattice bonds in the framework of an exact analytical approach based on the Kramers--Wannier transfer matrix method. Expressions for the entropy, heat capacity, and spontaneous magnetization of the lattice are obtained, including the residual (zero-temperature) entropy and residual (zero-temperature) spontaneous magnetization of the system. The existence of magnetic frustrations in such a model and their influence on the behavior of the thermodynamic functions of the system are shown. The new and most important result of our study is related to the description of the possible coexistence of frustrations and long-range magnetic order in partially ordered spin systems.

cond-mat.stat-mech↗

arXiv2022

Frustrations on decorated planar lattices in Ising model

We study the frustration properties of the Ising model on several decorated lattices with arbitrary numbers of decorating spins on all bonds of the lattice within an exact analytical approach based on the Kramers--Wannier transfer-matrix technique. The existence of magnetic frustrations in such situations and their influence on the behavior of the thermodynamic functions of systems is shown. The most important result of our study is related to the description of the possible coexistence of frustrations and long-range magnetic order in partially ordered spin systems.

cond-mat.stat-mech↗

arXiv2022

Frustrations and orderings in Ising chain with multiple interactions

The frustration properties of the Ising model on a one-dimensional monoatomic equidistant lattice are investigated taking into account the exchange interactions of atomic spins at the sites of the first (nearest), second (next-nearest) and third neighbors. The exact solution of the model was obtained using the Kramers--Wannier transfer matrix method. The types of magnetic ordering of the ground state of the model are determined, and a magnetic phase diagram is constructed. Criteria are formulated for the occurrence of magnetic frustrations in the presence of competition between the energies of exchange interactions. Non-zero entropy values in the ground state of the frustrated system were found.

cond-mat.stat-mech↗

arXiv2022

Diffuse scattering on Ising chain with competing interactions

We considered the Ising 1D chain in an external magnetic field taking into account the nearest and next-nearest neighbor interactions. By the method of Kramers--Wannier transfer-matrix, the rigorous analytical expression for Fourier-transform of pair spin-spin correlation function was obtained, and the temperature evolution of the scattering was analyzed for various relations of exchange parameters.

cond-mat.stat-mech↗

arXiv2022

Frustration and ordering in Ising chain in an external magnetic field with third-neighbor interactions

In this paper, the frustration properties of the Ising model on a one-dimensional monoatomic equidistant lattice in an external magnetic field are investigated, taking into account the exchange interactions of atomic spins at the sites of the first, second, and third neighbors. Exact analytical expressions for the thermodynamic functions of the system are obtained by the Kramers--Wannier transfer-matrix method. A magnetic phase diagram of the ground state of such a spin system is constructed and studied thoroughly. The points and lines of frustrations of the system depending on the values and signs of exchange interactions and on an external magnetic field are found. The criteria for the occurrence of magnetic frustrations in the presence of competition between the energies of exchange interactions and an external magnetic field are formulated. The peculiar features are investigated and the values of entropy and magnetization of the ground state of this model are obtained in the frustration regime and beyond it. Various types of behavior of entropy, magnetization, and magnetic susceptibility depending on the model parameters are revealed.

cond-mat.stat-mech↗

arXiv2020

Frustrations in the Ising chain with the third-neighbor interactions

We study the frustration properties of the Ising model on a one-dimensional monoatomic equidistant lattice, taking into account the exchange interactions of atomic spins at the sites of the nearest, next-nearest, and third neighbors. The exact analytical expressions for the thermodynamic functions of the system are obtained using the Kramers--Wannier transfer matrix technique. Criteria for the emergence of magnetic frustrations in the presence of competition between the energies of exchange interactions are formulated. The points and intervals of the existence of frustrations, which depend on the values and signs of the exchange interactions, are found. The features of the entropy and heat capacity of this model in the frustration regime and its vicinity are investigated. Non-zero entropy values of the ground state of a frustrated system, as well as a two-peak temperature structure of the heat capacity in the vicinity of the frustration point, are found.

cond-mat.stat-mech↗

arXiv2014

Magnetocaloric effect and frustrations in one-dimensional magnets

In this paper, we investigated the magnetocaloric effect (MCE) in one-dimensional magnets with different types of ordering in the Ising model, Heisenberg, XY-model, the standard, planar, and modified Potts models. Exact analytical solutions to MCE as functions of exchange parameters, temperature, values and directions of an external magnetic field are obtained. The temperature and magnetic field dependences of MCE in the presence of frustrations in the system in a magnetic field are numerically computed in detail.

cond-mat.str-el↗

arXiv2011

Evolution of the spectrum and the metal-insulator transition in local approximations for many-electron models

In the framework of the many-electron s-d exchange model and Hubbard model, self-consistent equations are derived for the one-particle retarded Green's function in the many-electron Hubbard X-operator representation. We analyze the general structure of the single-site approximations and their connection with the coherent potential approximation (CPA) and dynamic effective field theory (DMFT). Using the self-consistent approximation, we examine in detail the picture of the evolution of the electron spectrum with the model parameters (coupling constants, the concentration of charge carriers). The influence of various factors (Kondo many-electron scattering, smearing due to damping, dynamics of localized moment subsystem) on the shape of the density of states N(E) in the interacting system is investigated. It is shown that the use of the locator representation allows to avoid in some cases the non-analyticity in approximate expressions for the Green's functions. Our approach enables one to reproduce, at certain values of the parameters, three-peak structure of N(E) near the metal-insulator transition.

cond-mat.str-el↗

arXiv2011

Ferromagnetism, spiral magnetic structures and phase separation in the two-dimensional Hubbard model

The quasistatic approximation and equation-of-motion decoupling for the electron Green's functions are applied to trace the effect of electronic dispersion and electron correlations on the ferromagnetism of two-dimensional itinerant-electron systems. It is found that next-nearest-neighbor hopping t' is of crucial importance for ferromagnetism formation yielding the magnetic phase diagram which is strongly asymmetric with respect to half-filling. At small t' in the vicinity of half-filling the ferromagnetic phase region is restricted by the spin-density wave instability, and far from half-filling by one-particle (spin-polaron) instability. At t' close to t/2 ferromagnetism is stabilized at moderate Hubbard U due to substantial curvature of the Fermi surface which passes in the vicinity of the van Hove singularity points. The results obtained are of possible importance for high-T_c compounds and layered ruthenates.

cond-mat.str-el↗

arXiv2010

Ferromagnetism in the Highly-Correlated Hubbard Model

The Hubbard model with strong correlations is treated in the many-electron representation of Hubbard's operators. The regions of stability of saturated and non-saturated ferromagnetism in the n-U plane for the square and simple cubic lattices are calculated. The role of the bare density of states singularities for the magnetic phase diagram is discussed. A comparison with the results of previous works is performed.

cond-mat.str-el↗

arXiv2006

Single-particle spectrum for a model of fermions interacting with two-level local excitations on a lattice: A dynamical CPA approach

The problem of motion of a single electron interacting with a periodic lattice of two-level systems is investigated within a spinless fermion model. The Green's function is calculated in a single-site dynamical coherent potential approximation which is equivalent to DMFT. The picture of one-electron density of states is obtained for various values of the tunnel splitting and coupling between the electron and two-level system. The occurrence of a band splitting with increase of the coupling is demonstrated.

cond-mat.str-el↗

arXiv2004

Density-of-states picture and stability of ferromagnetism in the highly-correlated Hubbard model

The problem of stability of saturated and non-saturated ferromagnetism in the Hubbard model is considered in terms of the one-particle Green's functions. Approximations by Edwards and Hertz and some versions of the self-consistent approximations based on the 1/z-expansion are considered. The account of longitudinal fluctuations turns out to be essential for description of the non-saturated state. The corresponding pictures of density of states are obtained. "Kondo" density-of-states singularities owing to spin-flip processes are analyzed. The critical electron concentrations for instabilities of saturated ferromagnetism and paramagnetic state are calculated for various lattices. Drawbacks of various approximations are discussed. A comparison with the results of previous works is performed.

cond-mat.str-el↗

arXiv2001

Metal-insulator transition in the Hubbard model: a simple description including the Kondo effect

The electron spectrum structure in the half-filled Hubbard model is considered in terms of the one-particle Green's functions within many-electron representation. A simple analytical generalization of the single-site Hubbard-III approximation is obtained, which takes into account the Fermi excitations (Kondo terms). The problem of the metal-insulator transition is investigated. The occurrence of a three-peak density-of-states structure including the "Kondo" peak at the Fermi level is discussed. A comparison with large-d calculations is performed.

cond-mat.str-el↗

arXiv2000

The Kondo effect in periodic narrow-band systems

The Kondo divergences owing to interaction of current carriers with local moments in highly correlated electron systems are considered within the Hubbard and s-d exchange models with infinitely strong on-site interaction, the many-electron Hubbard representation being used. The picture of density of states containing a peak at the Fermi level is obtained. Various forms of the self-consistent approximation are used. The problem of the violation of analytical properties of the Green's function is discussed. Smearing of the "Kondo" peak owing to spin dynamics and finite temperatures is investigated.

cond-mat.str-el↗