arXiv subjects

Jozef Strečka

Publications and source records attributed to Jozef Strečka.

24 records · Page 2Linked to original sources

arXiv2018

Enhanced magnetoelectric effect of exactly solved spin-electron model on a doubly decorated square lattice in vicinity of a continuous phase transition

Magnetoelectric properties of a coupled spin-electron model on a doubly decorated square lattice in an external electric field applied along the crystallographic axis [11] are rigorously examined with the help of generalized decoration-iteration transformation. The phase diagram, spontaneous magnetization and electric polarization are exactly calculated and their dependencies are comprehensively investigated under a concurrent influence of temperature and electric field. It is found that the electric field mostly stabilizes at zero temperature the spontaneous antiferromagnetic order with respect to the ferromagnetic one. At finite temperatures the external electric field gradually suppresses a spontaneous ferromagnetic (antiferromagnetic) order emergent close to a quarter (half) filling. An enhanced magnetoelectric response is detectable in vicinity of a continuous phase transition at which the spontaneous magnetization vanishes and the electric polarization displays a weak-type singularity. It is demonstrated that reentrant phase transitions of the ferromagnetic or antiferromagnetic phase may be induced at moderate values of the electric field, which simultaneously produces a sharp kink in a critical line of the ferromagnetic phase nearby a quarter filling.

cond-mat.str-el↗

arXiv2018

Rise and Fall of Reentrant Phase Transitions in a Coupled Spin-Electron Model on a Doubly Decorated Honeycomb Lattice

Phase diagrams and spontaneous magnetization are rigorously calculated for a coupled spin-electron model on a doubly decorated honeycomb lattice, which accounts for a quantum-mechanical hopping of the mobile electrons on decorating sites, the nearest-neighbor Ising coupling between mobile electrons and localized spins, as well as, the further-neighbor Ising coupling between the localized spins placed on nodal sites. The spontaneously ordered ferromagnetic phase, spontaneously ordered antiferromagnetic phase and disordered paramagnetic phase emerge in a phase diagram depending on an electron filling of the decorating sites, a relative size of the hopping term and both considered coupling constants. It is evidenced that a nature and size of the further-neighbor Ising coupling between the localized spins basically influences rise and fall of reentrant transitions close to a phase boundary between the paramagnetic phase and both spontaneously ordered phases.

cond-mat.stat-mech↗

arXiv2017

Magnetization processes and existence of reentrant phase transitions in coupled spin-electron model on doubly decorated planar lattices

An alternative model for a description of magnetization processes in coupled 2D spin-electron systems has been introduced and rigorously examined using the generalized decoration-iteration transformation and the corner transfer matrix renormalization group method. The model consists of localized Ising spins placed on nodal lattice sites and mobile electrons delocalized over the pairs of decorating sites. It takes into account a hopping term for mobile electrons, the Ising coupling between mobile electrons and localized spins as well as the Zeeman term acting on both types of particles. The ground-state and finite-temperature phase diagrams were established and comprehensively analyzed. It was found that the ground-state phase diagrams are very rich depending on the electron hopping and applied magnetic field. The diversity of magnetization curves can be related to intermediate magnetization plateaus, which may be continuously tuned through the density of mobile electrons. In addition, the existence of several types of reentrant phase transitions driven either by temperature or magnetic field was proven.

cond-mat.str-el↗

arXiv2017

Reentrant phase transitions of a coupled spin-electron model on doubly decorated planar lattices with two or three consecutive critical points

The generalized decoration-iteration transformation is adapted for the exact study of a coupled spin-electron model on 2D lattices in which localized Ising spins reside on nodal lattice sites and mobile electrons are delocalized over pairs of decorating sites. The model takes into account a hopping term for mobile electrons, the Ising coupling between mobile electrons and localized spins as well as the Ising coupling between localized spins ($J'$). The ground state, spontaneous magnetization and specific heat are examined for both ferromagnetic ($J'>0$) as well as antiferromagnetic ($J'<0$) interaction between the localized spins. Several kinds of reentrant transitions between the paramagnetic ($P$), antiferromagnetic ($AF$) and ferromagnetic ($F$) phases have been found either with a single critical point, or with two consecutive critical points ($P-AF$/$F-P$) and three successive critical points $AF/F-P-F/AF-P$. Striking thermal variations of the spontaneous magnetization depict a strong reduction due to the interplay between annealed disorder and quantum fluctuations in addition to the aforementioned reentrance. It is shown that the specific heat displays diverse thermal dependencies including finite cusps at the critical temperatures.

cond-mat.str-el↗

arXiv2017

The influence of further-neighbor spin-spin interaction on a ground state of 2D coupled spin-electron model in a magnetic field

An exhaustive ground-state analysis of extended two-dimensional (2D) correlated spin-electron model consisting of the Ising spins localized on nodal lattice sites and mobile electrons delocalized over pairs of decorating sites is performed within the framework of rigorous analytical calculations. The investigated model, defined on an arbitrary 2D doubly decorated lattice, takes into account the kinetic energy of mobile electrons, the nearest-neighbor Ising coupling between the localized spins and mobile electrons, the further-neighbor Ising coupling between the localized spins and the Zeeman energy. The ground-state phase diagrams are examined for a wide range of model parameters for both ferromagnetic as well as antiferromagnetic interaction between the nodal Ising spins and non-zero value of external magnetic field. It is found that non-zero values of further-neighbor interaction leads to a formation of new quantum states as a consequence of competition between all considered interaction terms. Moreover, the new quantum states are accompanied with different magnetic features and thus, several kinds of discontinuous field-driven phase transitions are observed.

cond-mat.str-el↗

arXiv2014

Ground state, magnetization process and magnetocaloric effect of the exactly tractable spin-electron tetrahedral chain

A hybrid spin-electron system on one-dimensional tetrahedral chain, in which the localized Ising spin regularly alternates with the mobile electron delocalized over three lattice sites, is exactly investigated using the generalized decoration-iteration transformation. The system exhibits either the ferromagnetic or antiferromagnetic ground state depending on whether the ferromagnetic or antiferromagnetic interaction between the Ising spins and mobile electrons is considered. The enhanced magnetocaloric effect during the adiabatic demagnetization suggests a potential use of the investigated system for low-temperature magnetic refrigeration.

cond-mat.str-el↗