arXiv subjects

M. Žukovič

Publications and source records attributed to M. Žukovič.

At least 19 recordsLinked to original sources

arXiv2025

Frustration-driven topological textures on the honeycomb lattice: antiferromagnetic meron-antimeron and skyrmion crystals emerging from spiral spin liquids

Skyrmions -- topologically nontrivial magnetic quasi-particles -- can emerge in two-dimensional chiral magnets due to moderate or high strength of the Dzyaloshinskii-Moriya (DM) interaction. In this work, we show that the inclusion of weak next-nearest-neighbor DM interaction in the frustrated $J_1$-$J_2$ honeycomb-lattice Heisenberg antiferromagnet leads to the emergence of field-induced incommensurate antiferromagnetic meron-antimeron pairs and antiferromagnetic skyrmion structures. Using the Luttinger-Tisza approximation and large-scale Monte Carlo simulations, we report that for lower frustration values, antiferromagnetic meron-antimeron pair crystal and gas phases emerge within a small magnetic field window. In these meron phases, the fundamental unit consists of a meron-antimeron pair residing on different sublattices of the honeycomb lattice, even in the gas phase, where they exhibit greater mobility. For larger frustration, a two-layer-like three-sublattice antiferromagnetic skyrmion crystal phase is stabilized over a wider magnetic field range. At lower temperatures, this region splits into two distinct antiferromagnetic skyrmion phases with skyrmions of different sizes, reflecting the influence of frustration and thermal effects on the stabilization of these topological textures. Interestingly, both meron and skyrmion low-temperature phases connect to spiral spin liquid phases of the honeycomb lattice at higher temperatures. Additionally, we analyze the emergent single-$q$ and double-$q$ phases at low temperatures, constructing a comprehensive phase diagram.

cond-mat.str-el↗

arXiv2022

Fast gap-filling of massive data by local-equilibrium conditional simulations on GPU

The ever-growing size of modern space-time data sets, such as those collected by remote sensing, requires new techniques for their efficient and automated processing, including gap-filling of missing values. CUDA-based parallelization on GPU has become a popular way to dramatically increase computational efficiency of various approaches. Recently, we have proposed a computationally efficient and competitive, yet simple spatial prediction approach inspired from statistical physics models, called modified planar rotator (MPR) method. Its GPU implementation allowed additional impressive computational acceleration exceeding two orders of magnitude in comparison with CPU calculations. In the current study we propose a rather general approach to modelling spatial heterogeneity in GPU-implemented spatial prediction methods for two-dimensional gridded data by introducing spatial variability to model parameters. Predictions of unknown values are obtained from non-equilibrium conditional simulations, assuming ``local'' equilibrium conditions. We demonstrate that the proposed method leads to significant improvements in both prediction performance and computational efficiency.

stat.CO↗

arXiv2022

Spontaneous antiferromagnetic skyrmion/antiskyrmion lattice and spiral spin liquid states in the frustrated triangular lattice

Magnetic skyrmions are topological quasiparticles of great interest for data storage applications because of their small size, high stability, and ease of manipulation via electric current. Antiferromagnetic (AF) skyrmions, with new features and huge benefits (ultra-small skyrmion sizes, no transverse deflection and efficient manipulation), have recently become the subject of intense focus. Here we show that a spontaneous antiferromagnetic skyrmion/antiskyrmion lattice (AF-SkL/ASkL) emerges in the classical Heisenberg antiferromagnet on the triangular-lattice under magnetic fields, taking only exchange interactions up to third nearest neighbors ($J_1$-$J_2$-$J_3$). By means of the Luttinger-Tisza approximation and large scale Monte-Carlo simulations (combining Parallel-Tempering and overrelaxation with the Metropolis algorithm), we present a rich $J_2$-$J_3$ magnetic phase diagram including exotic multiple-q phases, degenerate states and a spontaneous AF-SkL/ASkL lattice at intermediate magnetic fields. In addition, we show that at zero magnetic field, exotic spin liquid states with ring-like degeneracy emerge at intermediate temperatures, which are broken by thermal fluctuations selecting different multiple-q states. These findings greatly enrich the research on antiferromagnetic skyrmions in centrosymmetric materials or lattices including relatively weak Dzyaloshinskii-Moriya interaction.

cond-mat.str-el↗

arXiv2022

Road to zero-field antiferromagnetic skyrmions in a frustrated AFM/FM heterostructure

We demonstrate a mechanism of significant reduction, including complete elimination, of the external magnetic field required for the stabilization of a skyrmion lattice (SkX) phase in a frustrated triangular Heisenberg antiferromagnet (AFM) with the Dzyaloshinskii-Moriya interaction. It is achieved by coupling of such a AFM plane to a reference ferromagnetic (FM) layer, which generates an effective field cooperating with the external magnetic field. If the FM layer shows some axial single-ion anisotropy then the effective field can also be generated in zero external field due to a spontaneous FM long-range ordering. Then a sufficiently large interlayer coupling can fully substitute the external magnetic field and the SkX phase in the AFM layer can be stabilized even in zero external field.

cond-mat.str-el↗

arXiv2022

Absence of long-range order in a three-dimensional stacked Ising antiferromagnet on kagome lattice

We study the possibility of long-range ordering (LRO) in a 3D system of vertically stacked layers of Ising antiferromagnet on a kagome lattice (SIAKL). Monte Carlo simulations are carried out for a varying interlayer coupling strength and a finite-size scaling analysis is performed for selected cases. Unlike in the related Ising system on a triangular lattice, in which even a finite number of the layers can stabilize LRO, or the Heisenberg system on the same kagome lattice, in which LRO emerged in 3D for a sufficient strength of the interlayer coupling, no LRO could be observed in the present model. This makes SIAKL a rare example of a 3D Ising paramagnet composed of frustrated layers coupled by unfrustrated interaction.

cond-mat.stat-mech↗

arXiv2021

Formation and growth of skyrmion crystal phase in a frustrated Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interaction

We study the formation and growth of a skyrmion crystal (SkX) phase in a frustrated antiferromagnetic Heisenberg model on a triangular lattice with Dzyaloshinskii-Moriya interaction (DMI) in the presence of an external magnetic field. We build phase diagrams in the temperature-field parameter plane, featuring first-order phase transitions and tricritical points, and study their evolution with the increasing DMI strength. It is found that already relatively small DMI intensity can lead to the appearance of the SkX phase at low temperatures in the vicinity of the meeting point of the remaining helical, coplanar up-up-down, and vortical-like ordered phases. By means of a parallel tempering (PT) Monte Carlo algorithm we find that the minimum value of DMI, at which the skyrmion phase emerges, $D_t \approx 0.02$, is one order of magnitude smaller then previously reported. We demonstrate the efficiency of PT in reliable and precise location of the phase boundaries between different phases separated by either very large (strong first-order transition) or barely detectable energy barriers, where the standard Monte Carlo approach may easily fail to find a stable solution.

cond-mat.str-el↗

arXiv2021

Stability of skyrmion crystal phase in antiferromagnetic triangular lattice with DMI and single-ion anisotropy

We study a frustrated antiferromagnetic Heisenberg model on a triangular lattice with the Dzyaloshinskii-Moriya interaction (DMI) in the presence of an external magnetic field and a single-ion anisotropy. Phase diagrams in the temperature-field plane for both easy-axis and easy-plane anisotropy of a varying strength are constructed in the regimes of a moderate and strong DMI by parallel tempering Monte Carlo simulations. For the considered range of parameters the phase diagrams featuring up to four ordered phases are identified. A skyrmion lattice (SkX) phase is found to be stabilized within some temperature and field window for sufficiently large DMI and not too strong anisotropy. For the systems with moderate (larger) DMI, a small easy-plane (easy-axis) anisotropy is concluded to be beneficial by extending (shifting) the field window of the SkX appearance to lower values. The Metropolis dynamics is employed to probe the persistence of SkX upon quenching the field to zero or small finite values. The most favorable conditions for the skyrmions persistence are confirmed at low temperatures, small DMI and small easy-plane anisotropy values.

cond-mat.stat-mech↗

arXiv2021

Phase diagrams of antiferromagnetic $XY$ model on a triangular lattice with higher-order interactions

We study effects of higher-order antinematic interactions on the critical behavior of the antiferromagnetic (AFM) $XY$ model on a triangular lattice, using Monte Carlo simulations. The parameter $q$ of the generalized antinematic (ANq) interaction is found to have a pronounced effect on the phase diagram topology by inducing new quasi-long-range ordered phases due to competition with the conventional AFM interaction as well as geometrical frustration. For values of $q$ divisible by 3 the conflict between the two interactions results in a frustrated canted AFM phase appearing at low temperatures wedged between the AFM and ANq phases. For $q$ nondivisible by 3 with the increase of $q$ one can observe the evolution of the phase diagram topology featuring two ($q=2$), three ($q=4,5$) and four ($q \geq 7$) ordered phases. In addition to the two phases previously found for $q=2$, the first new phase with solely AFM ordering arises for $q=4$ in the limit of strong AFM coupling and higher temperatures by separating from the phase with the coexisting AFM and ANq orderings. For $q=7$ another phase with AFM ordering but multimodal spin distribution in each sublattice appears at intermediate temperatures. All these algebraic phases also display standard and generalized chiral long-range orderings, which decouple at higher temperatures in the regime of dominant ANq (AFM) interaction for $q \geq 4$ ($q \geq 7$) preserving only the generalized (standard) chiral ordering.

cond-mat.stat-mech↗

arXiv2021

Critical properties of the frustrated Ising model on a honeycomb lattice: A Monte Carlo study

Critical and in the highly frustrated regime also dynamical properties of the $J_1-J_2$ Ising model with competing nearest-neighbor $J_1$ and second-nearest-neighbor $J_2$ interactions on a honeycomb lattice are investigated by standard Monte Carlo and parallel tempering simulations. The phase boundary is determined as a function of the coupling ratio for the phase transition between the paramagnetic and ferromagnetic states within $R \equiv J_2/|J_1| \in [-1/4,0]$. It is confirmed that at least for $R \geq -0.2$ the transition remains second-order and complies with the standard Ising universality class. In the highly frustrated regime of $R < -0.2$ and low temperatures the system tends to freeze to metastable domain states, separated by large energy barriers, which show extremely sluggish dynamics. The resulting huge equilibration and autocorrelation times hinder the analysis of critical properties and thus the character of the transition in this region remains to be determined.

cond-mat.stat-mech↗

arXiv2020

Absence of long-range order in a general spin-$S$ kagome lattice Ising antiferromagnet

The possibility of the emergence of some kind of long-range ordering (LRO) due to the increase of multiplicity of the local degrees of freedom (spin value $S$) is studied in an Ising antiferromagnet on a kagome lattice (IAKL) by Monte Carlo simulation. In particular, the critical exponent of the spin correlation function, obtained from a finite-size scaling analysis, is evaluated for various values of $S$, including $S=\infty$, with the goal to determine whether there exists some threshold value of the spin $S_C$ above which the system would show true or quasi-LRO, similar to a related model on a triangular lattice (IATL). It is found that, unlike in the IATL case, the IAKL model remains disordered for any spin value and any finite temperature.

cond-mat.stat-mech↗

arXiv2020

New ordered phase in geometrically frustrated generalized $XY$ model

Critical properties of a geometrically frustrated generalized $XY$ model with antiferromagnetic (AFM) and third-order antinematic (AN3) couplings on a triangular lattice are studied by Monte Carlo simulation. It is found that such a generalization leads to a phase diagram consisting of three different quasi-long-range ordered (QLRO) phases. Compared to the model with the second-order antinematic (AN2) coupling, besides the AFM and AN3 phases which appear in the limits of relatively strong AFM and AN3 interactions, respectively, it includes an additional complex canted antiferromagnetic (CAFM) phase. It emerges at lower temperatures, wedged between the AFM and AN3 phases, as a result of the competition between the AFM and AN3 couplings, which is absent in the model with the AN2 coupling. The AFM-CAFM and AN3-CAFM phase transitions are concluded to belong to the weak Ising and weak three-state Potts universality classes, respectively. Additionally, all three QLRO phases also feature true LRO of the standard and generalized chiralities, which both vanish simultaneously at second-order phase transitions with non-Ising critical exponents and the critical temperatures slightly higher than the magnetic and nematic order-disorder transition temperatures.

cond-mat.stat-mech↗

arXiv2019

Magnetism of the diluted Ising antiferromagnet in a magnetic field on the Kagome lattice: single-spin cluster approximation

An effective-field theory based on the single-spin cluster has been used to study of a diluted spin-$1/2$ Ising antiferromagnet on the Kagome lattice with nearest-neighbor interactions. We observe five plateaus in the magnetization curve of the diluted antiferromagnet when a magnetic field is applied which is in agreement with Monte Carlo calculation. The effect of the site-dilution on the magnetic susceptibility is also investigated and discussed. In particular, we have found that the frustrated Kagome lattice inverse susceptibility fall to zero at $0$K.

cond-mat.stat-mech↗

arXiv2019

Emergence of a Skyrmion Phase in a Frustrated Heisenberg Antiferromagnet with Dzyaloshinskii-Moriya Interaction

We study formation of a periodical structure of quasiparticle-like magnetic configurations with non-trivial topological charge, known as a magnetic skyrmion phase, on a frustrated triangular lattice antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya interaction (DMI) by means of Monte Carlo simulations. The existence of such a phase, formed on the three interpenetrating sublattices, has been demonstrated for a sufficiently large strength of DMI. The goal of the present investigation is to establish the minimum values of both the DM interaction strength as well as the magnetic field intensity at which such a skyrmion phase can exist at very low temperatures (close to zero). We find that the skyrmion phase emerges above the DMI parameter value of $D = 0.2$ and persists within the field intensity $2 \lesssim h < 4.5$.

cond-mat.str-el↗

arXiv2019

Spin-glass-like ordering in a frustrated $J_1-J_2$ Ising antiferromagnet on a honeycomb lattice

We study the nature of a low-temperature phase in the frustrated honeycomb-lattice Ising model with first- and second-neighbor antiferromagnetic (AF) interactions, $J_1$ and $J_2$, respectively, for $R = J_2/J_1 > 1/4$. It is known that for $R < 1/4$ there is a phase transition at low temperatures to the AF phase. Nevertheless, little is known about the critical behavior of the model for $R > 1/4$, except for recent effective field results which detected no phase transition down to zero temperature. Our Monte Carlo results suggest that for $R > 1/4$ there is at least one peculiar phase transition accompanied by a spin-glass-like freezing to a highly degenerate state consisting of frozen domains with stripe-type AF ordering separated by zero-energy domain walls. In spite of the local ordering within the respective domains there is no ordering among them and thus, unlike in the corresponding square-lattice model with $R > 1/2$, there is no conventional magnetic long-range ordering spanning the entire system.

cond-mat.stat-mech↗

arXiv2019

Magnetocaloric properties of an Ising antiferromagnet on a kagome lattice

Owing to a high degree of geometrical frustration an Ising antiferromagnet on a kagome lattice (IAKL) is known to exhibit no long-range ordering at any temperature, including the ground state. Nevertheless, at low temperatures it shows a strongly correlated, highly fluctuating regime known as a cooperative paramagnet or classical spin liquid. In the ground state it is characterized by a macroscopic degeneracy which translates to a relatively large value of the residual entropy. It has been shown that the presence of a macroscopic degeneracy associated with geometrical frustration below the saturation field can facilitate an enhanced magnetocaloric effect (MCE), which can exceed that of an ideal paramagnet with equivalent spin by more than an order of magnitude. In the present study we investigate magnetic and magnetocaloric properties of IAKL by Monte Carlo simulation. In particular, we calculate the entropy of the system using the thermodynamic integration method and evaluate quantities which characterize MCE, such as the isothermal entropy and adiabatic temperature changes in a varying magnetic field. It is found that IAKL shows the most interesting magnetocaloric properties at low temperatures and moderate magnetic fields, suggesting its potential to be used in technological applications for low-temperature magnetic refrigeration.

cond-mat.stat-mech↗

arXiv2019

Magnetocaloric properties of frustrated tetrahedra-based spin nanoclusters

Magnetization, entropy and magnetocaloric properties of various geometrically frustrated tetrahedra-based Ising antiferromagnetic nanoclusters with corner-, edge-, and face-sharing topologies are studied by exact enumeration. It is found that the studied properties strongly depend on the nanocluster topology and can be very different from those of a single tetrahedron as well as the pyrochlore lattice formed by an infinite number of corner-sharing tetrahedra. From the magnetocaloric point of view an important difference from the latter two systems is the absence of the ground-state zero-magnetization plateau in most of the studied structures, which at low temperatures facilitates emergence of a giant magnetocaloric effect in a vanishing magnetic field in the adiabatic demagnetization process. Magnetic systems with such properties might be suitable candidates for technological application as efficient refrigerators to ultra-low temperatures.

cond-mat.str-el↗

arXiv2018

Phase Diagram of the $J_1$ - $J_2$ Frustrated Anisotropic Antiferromagnet with Spin $S=1$ on the Quadratic Lattice

In the paper the phase diagram of $J_1-J_2$ frustrated antiferromagnet with spin $S=1$ and single-ion anisotropy is studied on the planar quadratic lattice in the cluster approximation. The Bogolyubov inequality is adopted for the Gibbs energy calculation for the case of $2 \times 2$ and $4 \times 4$ clusters. On this basis, the ranges of existence of the anfiferromagnetic, superantiferromagnetic and paramagnetic phases are investigated for the antiferromagnetic nearest-neighbour ($J_1<0$) and next-nearest-neighbour ($J_2<0$) interactions. In particular, the occurrence of tricritical and triple points is discussed and a comparison between the results for $2 \times 2$ and $4 \times 4$ clusters is made. The results are also compared with the classical MFA method, adopted here for the model in question, as well as with selected literature results for particular choices of interaction parameters.

cond-mat.stat-mech↗

arXiv2018

Thermodynamic and critical properties of an antiferromagnetically stacked triangular Ising antiferromagnet in a field

We study a stacked triangular lattice Ising model with both intra- and inter-plane antiferromagnetic interactions in a field, by Monte Carlo simulation. We find only one phase transition from a paramagnetic to a partially disordered phase, which is of second order and 3D XY universality class. At low temperatures we identify two highly degenerate phases: at smaller (larger) fields the system shows long-range ordering in the stacking direction (within planes) but not in the planes (stacking direction). Nevertheless, crossovers to these phases do not have a character of conventional phase transitions but rather linear-chain-like excitations.

cond-mat.stat-mech↗