A. Majhofer - Academia.edu (original) (raw)

Papers by A. Majhofer

Research paper thumbnail of Magnetic Properties of Chains of Spherical Nanoparticles with Cubic Magnetic Anisotropy: A Monte Carlo Study

Research paper thumbnail of Magnetic Behavior of ZnO Nanoparticles Doped with Co and Mn Ions

The II-IV valence nanoparticles with semiconducting, luminescent and magnetic properties are unde... more The II-IV valence nanoparticles with semiconducting, luminescent and magnetic properties are under ongoing research in modern spintronic. Magnetic properties of ZnO:Co and ZnO:Mn nanoparticles were investigated in this work. The influence of the concentration of the doping Mn/Co ions on the magnetization of Zn1-xMnxO and Zn1-xCoxO nanoparticles was experimentally obtained and analyzed. Superconducting quantum interface device (SQUID) with the applied magnetic field up to 7 T was used for determining the magnetization of ZnO:Co and ZnO:Mn nanapowders and compared with the pure ZnO nanopowder. Zink oxide nanopowders doped with 1%,15% Co and 1%,15% Mn were produced by the microwave solvothermal synthesis. The nanostructures of the particles were investigated by skeleton density, specific surface area (SSA), phase purity (XRD), lattice parameters, average particle size, crystal size distribution, scanning electron microscopy (SEM).

Research paper thumbnail of Surface Diffusion and Growth of Alloy Nanoclusters: A Monte Carlo Study

1. Introduction Molecular beam epitaxy has become an important tool to prepare ultrathin films an... more 1. Introduction Molecular beam epitaxy has become an important tool to prepare ultrathin films and nanostructures in nonequilibrium states that show novel properties distinctly different from the equilibrium bulk phases. Theoretically, the question arises how to relate the structural characteristics of the growing material to the incoming flux and temperature-dependent surface diffusion constants. This question is fairly well understood for one-component systems. By contrast, only few theoretical studies were devoted to the growth of binary alloy nanostructures, despite of the large interest in this field from the experimental and technological viewpoint. In this communication we present detailed kinetic Monte Carlo simulations of growing nanoclusters within a binary alloy model that allows arbitrary diffusion moves of atoms within an active zone near the cluster surface. Our model is designed to describe fcc-type alloys under growth in the (111) direction. The main motivation came ...

Research paper thumbnail of Spectral dimensionality and hyperscaling

Physical Review B, 1986

ABSTRACT

Research paper thumbnail of Magnetic interactions in an ensemble of cubic nanoparticles: A Monte Carlo study

Physical Review B, 2013

ABSTRACT The ensemble of spatially disordered and randomly oriented spherical monodispersed singl... more ABSTRACT The ensemble of spatially disordered and randomly oriented spherical monodispersed single-domain magnetic nanoparticles with cubic anisotropy was studied by the Monte Carlo method. In the presence of dipole-dipole interactions, the effect of both particle volume and interparticle separation was investigated with respect to the characteristic parameters of hysteresis loops and zero field cooled and field cooled magnetization curves. The coercive field and remanent magnetic moment were shown to depend strongly on the dimensionless parameter β=k_{B}T/(K_{1}V) (T temperature, V particle volume, K_{1} cubic anisotropy constant). It was revealed that strong dipole-dipole interactions suppress both the coercive field and the remanent magnetic moment of densely packed nanoparticles. Yet, the effect quickly diminishes with the increasing interparticle distances and becomes rather insignificant for separations exceeding three particle diameters. The blocking temperature was found to be weakly affected by dipolar interactions, but mainly governed via β, i.e., by the nanoparticle volume and the strength of crystalline anisotropy. The role of dipole-dipole interactions on magnetic properties of nanoparticles was further elucidated by a comparison of the simulation results for a single cluster with an infinite periodic arrangement of such clusters.

Research paper thumbnail of Structural and Magnetic Properties of Co‒Mn Codoped ZnO Nanoparticles Obtained by Microwave Solvothermal Synthesis

Crystals

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for... more Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1−x−y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm...

Research paper thumbnail of Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications

Acta Physica Polonica A, 2007

We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticle... more We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticles. The transmission electron microscopy, Mössbauer spectra (of iron) and SQUID magnetometry results demonstrate that the products of the synthesis contain metals and its carbides. The nanoparticles show ferromagnetic or superparamagnetic behavior at high temperatures, which is demanded for nano-spintronics applications.

Research paper thumbnail of Parameters of the deformed Woods-Saxon potential outside A=110-210 nuclei

Journal of Physics G: Nuclear Physics, 1979

The authors aim to reproduce single-particle level spins and parities of odd-A nuclei by adjustin... more The authors aim to reproduce single-particle level spins and parities of odd-A nuclei by adjusting the strength parameter lambda and the radius parameter (r0)so of the spin-orbit part of the deformed Woods-Saxon potential. Discussion is concentrated on the A>or=210 nuclei for which comparison with the extracted experimental level spacing is done. In addition, parametrisation of the deformed Woods-Saxon potential is discussed for A=40-110 nuclei (the nuclei with 110<or=A<or=210 were studied in a previous paper). In the adjustment procedure experimental equilibrium deformations beta 2 (and beta 4, if known) are taken into account. The parameters lambda and (r0)so are subjected to smooth variations only in order to preserve the overall character of the single-particle spectrum and not to disturb the sequence of spins and parities in the neighbouring nuclei.

Research paper thumbnail of Testing the interpretation of the γ-γ correlation experiments at high spins

Nuclear Instruments and Methods in Physics Research, 1982

Research paper thumbnail of Ordering kinetics in an fcc A 3 B binary alloy model: Monte Carlo studies

Physical Review B, 2003

Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder trans... more Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder transition in an fcc A3B binary alloy model following a temperature quench from the disordered phase. We observe two clearly distinct ordering scenarios depending on whether the final temperature T f falls above or below the ordering spinodal Tsp, which is deduced from simulations at equilibrium. For shallow quenches (T f > Tsp) we identify an incubation time τinc which characterizes the onset of ordering through the formation of overcritical ordered nuclei. The algorithm we use together with experimental information on tracer diffusion in Cu3Au alloys allows us to estimate the physical time scale connected with τinc in that material. Deep quenches, T f < Tsp, result in spinodal ordering. Coarsening processes at long times proceed substantially slower than predicted by the Lifshitz-Allen-Cahn t 1/2 law. Structure factors related to the geometry of the two types of domain walls that appear in our model are found to be consistent with Porod's law in one and two dimensions.

Research paper thumbnail of Monte Carlo simulation of subsurface ordering kinetics in an fcc alloy model

Physical Review B, 2001

Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate... more Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate the kinetics of surface-induced ordering processes close to the (001) surface of an fcc A3Balloy. After a sudden quench into the ordered phase with a final temperature above the ordering spinodal, T f > Tsp, the early time kinetics is dominated by a segregation front which propagates into the bulk with nearly constant velocity. Below the spinodal, T f < Tsp, motion of the segregation wave reflects a coarsening process which appears to be slower than predicted by the Lifschitz-Allen-Cahn law. In addition, in the front-penetrated region lateral growth differs distinctly from perpendicular growth, as a result of the special structure of antiphase boundaries near the surface. Our results are compared with recent experiments on the subsurface ordering kinetics at Cu3Au (001).

Research paper thumbnail of Effect of the Sign of Anisotropy Constants on the Properties of the System of Interacting Ferromagnetic Nanoparticles

Acta Physica Polonica A, 2016

We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrys... more We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrystalline anisotropy constants and the magnetic dipole-dipole interactions on the zero field cooled-field cooled magnetization experiments and hysteresis curves of a system of magnetic nanoparticles. Positive first cubic anisotropy constant K1 results in larger blocking temperatures and larger coercive fields of a system, while the second anisotropy constant K2 is practically of negligible importance for the phenomena investigated. Magnetic dipole-dipole interactions are important only in the most dense systems of particles and their effects practically disappear for systems where the distance between the closest particles exceeds three particle diameters.

Research paper thumbnail of Monte Carlo Simulations of Ferromagnetic Nanocomposites

Acta Physica Polonica A, 2012

We present results of Monte Carlo simulations of a model system of Co nanoparticles in an externa... more We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic eld. In our simulations we take into account the interaction with the external magnetic eld, the energy of crystallographic anisotropy and the dipoledipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature TB on particle and cluster size.

Research paper thumbnail of ac susceptibilities of a network of resistively shunted Josephson junctions with self-inductances

Physical review. B, Condensed matter, 1993

Research paper thumbnail of Irreversible magnetization effects in a network of resistively shunted tunnel junctions

Physical review. B, Condensed matter, 1991

We investigate the magnetic behavior of a two-dimensional network of resistively-shunted (zero-ca... more We investigate the magnetic behavior of a two-dimensional network of resistively-shunted (zero-capacitance) Josephson junctions, treating magnetic screening effects in a self-consistent manner. By this, we obtain stationary distributions of magnetic flux and hysteresis effects typical of single crystals or ceramic samples of high-Tc superconductors, depending upon the magnitude of the magnetic penetration depth lambdaJ.

Research paper thumbnail of Metastable effects and random polarities of magnetic moments in disordered systems of Josephson junctions

Physical review. B, Condensed matter, 1990

We use the Monte Carlo technique to simulate experiments on zero-field-cooled (ZFC) and field-coo... more We use the Monte Carlo technique to simulate experiments on zero-field-cooled (ZFC) and field-cooled (FC) superconducting samples. As our model we take a three-dimensional, strongly disordered system of Josephson junctions. For fields exceeding a certain critical value Hc1, we find well-pronounced differences between ZFC and FC magnetizations. At low temperatures, the diamagnetic response of FC samples cooled at Hc1 is

Research paper thumbnail of Thermally activated flux motion in a one-dimensional Josephson-junction array with self-inductances

Physical review. B, Condensed matter, 1996

We study relaxation of magnetic flux in a one-dimensional network of resistively shunted Josephso... more We study relaxation of magnetic flux in a one-dimensional network of resistively shunted Josephson junctions. Magnetic fields due to the currents induced in the system are taken into account via self-inductance coefficients. A master equation is derived that describes the stochastic motion of flux quanta among the different plaquettes of the network. Space- and time-dependent flux profiles are calculated within mean-field theory and also by a continuous-time Monte Carlo algorithm. The relevance of our results for the description of flux creep experiments in strongly inhomogeneous superconductors is pointed out.

Research paper thumbnail of Lattice-gas analog of density-functional theory: Application to ordering transitions

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1993

An alternative approach to ordering transitions in lattice gases is presented. Our approach can b... more An alternative approach to ordering transitions in lattice gases is presented. Our approach can be regarded as the lattice analog of the well-known freezing theory for continuous fluids based on density functionals. Specifically, we discuss ordering in a three-dimensional model involving repulsive forces up to second neighbors and compare our results with Monte Carlo simulations. The utility of our method is demonstrated further by calculating the structure of a planar interface between coexisting ordered and disordered phases. It is pointed out that our theory is a good starting point for investigating problems of the interfacial kinetics.

Research paper thumbnail of Density-functional method for lattice-gas problems

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1993

Research paper thumbnail of Monte Carlo simulations of a disordered, three-dimensional system of Josephson junctions

Physical Review B, 1989

Using a Monte Carlo technique we study properties of a disordered three-dimensional system of Jos... more Using a Monte Carlo technique we study properties of a disordered three-dimensional system of Josephson junctions. We focus on the anisotropy of the critical magnetic field and on relaxation processes in a zero-field-cooled sample.

Research paper thumbnail of Magnetic Properties of Chains of Spherical Nanoparticles with Cubic Magnetic Anisotropy: A Monte Carlo Study

Research paper thumbnail of Magnetic Behavior of ZnO Nanoparticles Doped with Co and Mn Ions

The II-IV valence nanoparticles with semiconducting, luminescent and magnetic properties are unde... more The II-IV valence nanoparticles with semiconducting, luminescent and magnetic properties are under ongoing research in modern spintronic. Magnetic properties of ZnO:Co and ZnO:Mn nanoparticles were investigated in this work. The influence of the concentration of the doping Mn/Co ions on the magnetization of Zn1-xMnxO and Zn1-xCoxO nanoparticles was experimentally obtained and analyzed. Superconducting quantum interface device (SQUID) with the applied magnetic field up to 7 T was used for determining the magnetization of ZnO:Co and ZnO:Mn nanapowders and compared with the pure ZnO nanopowder. Zink oxide nanopowders doped with 1%,15% Co and 1%,15% Mn were produced by the microwave solvothermal synthesis. The nanostructures of the particles were investigated by skeleton density, specific surface area (SSA), phase purity (XRD), lattice parameters, average particle size, crystal size distribution, scanning electron microscopy (SEM).

Research paper thumbnail of Surface Diffusion and Growth of Alloy Nanoclusters: A Monte Carlo Study

1. Introduction Molecular beam epitaxy has become an important tool to prepare ultrathin films an... more 1. Introduction Molecular beam epitaxy has become an important tool to prepare ultrathin films and nanostructures in nonequilibrium states that show novel properties distinctly different from the equilibrium bulk phases. Theoretically, the question arises how to relate the structural characteristics of the growing material to the incoming flux and temperature-dependent surface diffusion constants. This question is fairly well understood for one-component systems. By contrast, only few theoretical studies were devoted to the growth of binary alloy nanostructures, despite of the large interest in this field from the experimental and technological viewpoint. In this communication we present detailed kinetic Monte Carlo simulations of growing nanoclusters within a binary alloy model that allows arbitrary diffusion moves of atoms within an active zone near the cluster surface. Our model is designed to describe fcc-type alloys under growth in the (111) direction. The main motivation came ...

Research paper thumbnail of Spectral dimensionality and hyperscaling

Physical Review B, 1986

ABSTRACT

Research paper thumbnail of Magnetic interactions in an ensemble of cubic nanoparticles: A Monte Carlo study

Physical Review B, 2013

ABSTRACT The ensemble of spatially disordered and randomly oriented spherical monodispersed singl... more ABSTRACT The ensemble of spatially disordered and randomly oriented spherical monodispersed single-domain magnetic nanoparticles with cubic anisotropy was studied by the Monte Carlo method. In the presence of dipole-dipole interactions, the effect of both particle volume and interparticle separation was investigated with respect to the characteristic parameters of hysteresis loops and zero field cooled and field cooled magnetization curves. The coercive field and remanent magnetic moment were shown to depend strongly on the dimensionless parameter β=k_{B}T/(K_{1}V) (T temperature, V particle volume, K_{1} cubic anisotropy constant). It was revealed that strong dipole-dipole interactions suppress both the coercive field and the remanent magnetic moment of densely packed nanoparticles. Yet, the effect quickly diminishes with the increasing interparticle distances and becomes rather insignificant for separations exceeding three particle diameters. The blocking temperature was found to be weakly affected by dipolar interactions, but mainly governed via β, i.e., by the nanoparticle volume and the strength of crystalline anisotropy. The role of dipole-dipole interactions on magnetic properties of nanoparticles was further elucidated by a comparison of the simulation results for a single cluster with an infinite periodic arrangement of such clusters.

Research paper thumbnail of Structural and Magnetic Properties of Co‒Mn Codoped ZnO Nanoparticles Obtained by Microwave Solvothermal Synthesis

Crystals

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for... more Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1−x−y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm...

Research paper thumbnail of Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications

Acta Physica Polonica A, 2007

We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticle... more We succeeded in the arc-plasma synthesis of carbon-encapsulated Fe, Cr, and Mn-based nanoparticles. The transmission electron microscopy, Mössbauer spectra (of iron) and SQUID magnetometry results demonstrate that the products of the synthesis contain metals and its carbides. The nanoparticles show ferromagnetic or superparamagnetic behavior at high temperatures, which is demanded for nano-spintronics applications.

Research paper thumbnail of Parameters of the deformed Woods-Saxon potential outside A=110-210 nuclei

Journal of Physics G: Nuclear Physics, 1979

The authors aim to reproduce single-particle level spins and parities of odd-A nuclei by adjustin... more The authors aim to reproduce single-particle level spins and parities of odd-A nuclei by adjusting the strength parameter lambda and the radius parameter (r0)so of the spin-orbit part of the deformed Woods-Saxon potential. Discussion is concentrated on the A>or=210 nuclei for which comparison with the extracted experimental level spacing is done. In addition, parametrisation of the deformed Woods-Saxon potential is discussed for A=40-110 nuclei (the nuclei with 110<or=A<or=210 were studied in a previous paper). In the adjustment procedure experimental equilibrium deformations beta 2 (and beta 4, if known) are taken into account. The parameters lambda and (r0)so are subjected to smooth variations only in order to preserve the overall character of the single-particle spectrum and not to disturb the sequence of spins and parities in the neighbouring nuclei.

Research paper thumbnail of Testing the interpretation of the γ-γ correlation experiments at high spins

Nuclear Instruments and Methods in Physics Research, 1982

Research paper thumbnail of Ordering kinetics in an fcc A 3 B binary alloy model: Monte Carlo studies

Physical Review B, 2003

Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder trans... more Using an atom-vacancy exchange algorithm, we investigate the kinetics of the order-disorder transition in an fcc A3B binary alloy model following a temperature quench from the disordered phase. We observe two clearly distinct ordering scenarios depending on whether the final temperature T f falls above or below the ordering spinodal Tsp, which is deduced from simulations at equilibrium. For shallow quenches (T f > Tsp) we identify an incubation time τinc which characterizes the onset of ordering through the formation of overcritical ordered nuclei. The algorithm we use together with experimental information on tracer diffusion in Cu3Au alloys allows us to estimate the physical time scale connected with τinc in that material. Deep quenches, T f < Tsp, result in spinodal ordering. Coarsening processes at long times proceed substantially slower than predicted by the Lifshitz-Allen-Cahn t 1/2 law. Structure factors related to the geometry of the two types of domain walls that appear in our model are found to be consistent with Porod's law in one and two dimensions.

Research paper thumbnail of Monte Carlo simulation of subsurface ordering kinetics in an fcc alloy model

Physical Review B, 2001

Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate... more Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction model we investigate the kinetics of surface-induced ordering processes close to the (001) surface of an fcc A3Balloy. After a sudden quench into the ordered phase with a final temperature above the ordering spinodal, T f > Tsp, the early time kinetics is dominated by a segregation front which propagates into the bulk with nearly constant velocity. Below the spinodal, T f < Tsp, motion of the segregation wave reflects a coarsening process which appears to be slower than predicted by the Lifschitz-Allen-Cahn law. In addition, in the front-penetrated region lateral growth differs distinctly from perpendicular growth, as a result of the special structure of antiphase boundaries near the surface. Our results are compared with recent experiments on the subsurface ordering kinetics at Cu3Au (001).

Research paper thumbnail of Effect of the Sign of Anisotropy Constants on the Properties of the System of Interacting Ferromagnetic Nanoparticles

Acta Physica Polonica A, 2016

We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrys... more We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrystalline anisotropy constants and the magnetic dipole-dipole interactions on the zero field cooled-field cooled magnetization experiments and hysteresis curves of a system of magnetic nanoparticles. Positive first cubic anisotropy constant K1 results in larger blocking temperatures and larger coercive fields of a system, while the second anisotropy constant K2 is practically of negligible importance for the phenomena investigated. Magnetic dipole-dipole interactions are important only in the most dense systems of particles and their effects practically disappear for systems where the distance between the closest particles exceeds three particle diameters.

Research paper thumbnail of Monte Carlo Simulations of Ferromagnetic Nanocomposites

Acta Physica Polonica A, 2012

We present results of Monte Carlo simulations of a model system of Co nanoparticles in an externa... more We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic eld. In our simulations we take into account the interaction with the external magnetic eld, the energy of crystallographic anisotropy and the dipoledipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature TB on particle and cluster size.

Research paper thumbnail of ac susceptibilities of a network of resistively shunted Josephson junctions with self-inductances

Physical review. B, Condensed matter, 1993

Research paper thumbnail of Irreversible magnetization effects in a network of resistively shunted tunnel junctions

Physical review. B, Condensed matter, 1991

We investigate the magnetic behavior of a two-dimensional network of resistively-shunted (zero-ca... more We investigate the magnetic behavior of a two-dimensional network of resistively-shunted (zero-capacitance) Josephson junctions, treating magnetic screening effects in a self-consistent manner. By this, we obtain stationary distributions of magnetic flux and hysteresis effects typical of single crystals or ceramic samples of high-Tc superconductors, depending upon the magnitude of the magnetic penetration depth lambdaJ.

Research paper thumbnail of Metastable effects and random polarities of magnetic moments in disordered systems of Josephson junctions

Physical review. B, Condensed matter, 1990

We use the Monte Carlo technique to simulate experiments on zero-field-cooled (ZFC) and field-coo... more We use the Monte Carlo technique to simulate experiments on zero-field-cooled (ZFC) and field-cooled (FC) superconducting samples. As our model we take a three-dimensional, strongly disordered system of Josephson junctions. For fields exceeding a certain critical value Hc1, we find well-pronounced differences between ZFC and FC magnetizations. At low temperatures, the diamagnetic response of FC samples cooled at Hc1 is

Research paper thumbnail of Thermally activated flux motion in a one-dimensional Josephson-junction array with self-inductances

Physical review. B, Condensed matter, 1996

We study relaxation of magnetic flux in a one-dimensional network of resistively shunted Josephso... more We study relaxation of magnetic flux in a one-dimensional network of resistively shunted Josephson junctions. Magnetic fields due to the currents induced in the system are taken into account via self-inductance coefficients. A master equation is derived that describes the stochastic motion of flux quanta among the different plaquettes of the network. Space- and time-dependent flux profiles are calculated within mean-field theory and also by a continuous-time Monte Carlo algorithm. The relevance of our results for the description of flux creep experiments in strongly inhomogeneous superconductors is pointed out.

Research paper thumbnail of Lattice-gas analog of density-functional theory: Application to ordering transitions

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1993

An alternative approach to ordering transitions in lattice gases is presented. Our approach can b... more An alternative approach to ordering transitions in lattice gases is presented. Our approach can be regarded as the lattice analog of the well-known freezing theory for continuous fluids based on density functionals. Specifically, we discuss ordering in a three-dimensional model involving repulsive forces up to second neighbors and compare our results with Monte Carlo simulations. The utility of our method is demonstrated further by calculating the structure of a planar interface between coexisting ordered and disordered phases. It is pointed out that our theory is a good starting point for investigating problems of the interfacial kinetics.

Research paper thumbnail of Density-functional method for lattice-gas problems

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1993

Research paper thumbnail of Monte Carlo simulations of a disordered, three-dimensional system of Josephson junctions

Physical Review B, 1989

Using a Monte Carlo technique we study properties of a disordered three-dimensional system of Jos... more Using a Monte Carlo technique we study properties of a disordered three-dimensional system of Josephson junctions. We focus on the anisotropy of the critical magnetic field and on relaxation processes in a zero-field-cooled sample.