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P. N. Timonin

Publications and source records attributed to P. N. Timonin.

30 records · Page 2Linked to original sources
arXiv2009

Phenomenological theory of nonergodic phenomena in dipole- and spin-glasses

The path-dependent magnetizations (polarizations) and susceptibilities in dipole- and spin-glasses are described analytically for the standard protocols of temperature and field variations using the phenomenological Landau-type description of multiple metastable states in the nonergodic phases. The immediate manifestation of metastable states' multiplicity as staircases of magnetizations (polarizations) curves in the temperature cycling experiments is explained and described. The obtained results are in a reasonable qualitative agreement with the existing experimental data.

cond-mat.dis-nn↗
arXiv2008

Model of crystal growth with simulated self-attraction

The (1+1)-dimensional kinetic model of crystal growth with simulated self-attraction and random sequential or parallel dynamics is introduced and studied via Monte-Carlo simulations. To imitate the attraction of absorbing atoms the probability of deposition is chosen to depend on the number of the nearest-neighbor atoms surrounding the deposited atom so it increases with this number. As well the evaporation probabilities are chosed to roughly account for this self-attraction. The model exhibits the interface depinning transition with KPZ-type roughness behavior in the moving phase. The critical indices of the correlation lengths are $ν_\parallel = 0.82 \pm 0.03,{\rm{}}ν_ \bot = 0.55 \pm 0.02$ and the critical index of the growth velocity is $1.08 \pm 0.03$ indicating the new universality class of the depinning transition. The critical properties of the model do not depend on the type of dynamics implemented.

cond-mat.stat-mech↗
arXiv2008

Spin-glass instability of short-range spherical ferromagnet

In structurally disordered ferromagnets the weak random dipole-dipole exchange may transform the polydomain state into a spin-glass one. To some extent the properties of such phase in disordered isotropic ferromagnet can be qualitatively described by the spherical model with the short-range ferromagnetic interaction and weak frustrated infinite-range random-bond exchange. This model is shown to predict that spin-glass phase substitute the ferromagnetic one at the arbitrary small disorder strength and that its thermodynamics has some similarity to that of polydomain state along with some significant distinctions. In particular, the longitudinal susceptibility at small fields becomes frozen below transition point at a constant value depending on the disorder strength, while the third order nonlinear magnetic susceptibilitiy exhibits the temperature oscillations in small field near the transition point. The relation of these predictions to the experimental data for some disordered isotropic ferromagnets is discussed.

cond-mat.dis-nn↗
arXiv2008

Phase Transitions in Parallel Replication Process

The one-dimensional kinetic contact process with parallel update is introduced and studied by Monte Carlo simulations. This process is proposed to describe the plant population replication and epidemic disease spreading among them. The phase diagram of the model features the line of the second order transitions between absorbing and active phases. The numerical results for the critical index beta demonstrate its continuous variation along the transition line accompanied by the variations of the structural characteristics of limiting steady states. We conjecture the non-universality of the critical behavior of the model.

cond-mat.stat-mech↗
arXiv2006

Phase transitions in random magnetic bilayer

The influence of random interlayer exchange on the phase states of the simplest magnetic heterostructure consisting of two ferromagnetic Ising layers with large interaction radius is studied. It is shown that such system can exist in three magnetic phases: ferromagnetic, antiferromagnetic and ferrimagnetic. The possible phase diagrams and temperature dependencies of thermodynamic parameters are described. The regions of existence of the magnetic phases in external magnetic field are determined at zero temperature.

cond-mat.mtrl-sci↗
arXiv2005

Glassy phases in layered Ising magnets with random interlayer exchange

Thermodynamics of layered Ising magnet with the infinite-range ferromagnetic intralayer interaction and random exchange between nearest layers is considered. The case of zero average interlayer exchange is studied in detail. The inequilibrium thermodynamic potential is obtained near transition point and existence of numerous metastable states is shown. The thermodynamic properties of crystal in the simple periodic states are described. It is established that the evolution of the equilibrium magnetic state with growth of random exchange proceed over infinite series of first order transitions at which the number of magnetized layers and distance between them jump as well as homogeneous magnetization and susceptibility.

cond-mat.dis-nn↗
arXiv2004

Inhomogeneity-induced second-order phase transitions in Potts model on hierarchical lattices

The thermodynamics of the $q$-state Potts model with arbitrary $q$ on a class of hierarchical lattices is considered. Contrary to the case of the crystal lattices, it has always the second-order phase transitions. The analytical expressions fo the critical indexes are obtained, their dependencies on the structural lattice pararmeters are studied and the scailing relations among them are establised. The structural criterion of the inhomogeneity-induced transformation of the transition order is suggested. The application of the results to a description of critical phenomena in the dilute crystals and substances confined in porous media is discussed.

cond-mat.dis-nn↗
arXiv2003

On the thermodynamics of first-order phase transition smeared by frozen disorder

The simplified model of first-order transition in a media with frozen long-range transition-temperature disorder is considered. It exhibits the smearing of the transition due to appearance of the intermediate inhomogeneous phase with thermodynamics described by the ground state of the short-range random-field Ising model. Thus the model correctly reproduce the persistence of first-order transition only in dimensions d > 2, which is found in more realistic models. It also allows to estimate the behavior of thermodynamic parameters near the boundaries of the inhomogeneous phase.

cond-mat.dis-nn↗
arXiv2003

Pretransitional phenomena in dilute crystals with first-order phase transition

Pretransitional phenomena at first-order phase transition in crystals diluted by 'neutral' impurities (analogue of nonmagnetic atoms in dilute magnets) are considered. It is shown that field dependence of order parameter becomes nonanalytical in the stability region of the ordered phase, while smeared jumps of thermodynamic parameters and anomalous (non-exponential) relaxation appear near transition temperature of pure crystal.

cond-mat.dis-nn↗
arXiv2001

Metastable states in disordered Ising magnets in mean-field approximation

The mechanism of appearance of exponentially large number of metastable states in magnetic phases of disordered Ising magnets with short-range random exchange is suggested. It is based on the assumption that transitions into inhomogeneous magnetic phases results from the condensation of macroscopically large number of sparse delocalized modes near the localization threshold. The properties of metastable states in random magnets with zero ground state magnetization (dilute antiferromagnet, binary spin glass, dilute ferromagnet with dipole interaction) has been obtained in framework of this mechanism using variant of mean-field approximation. The relations between the characteristics of slow nonequilibrium processes in magnetic phases and thermodynamic parameters of metastable states are established.

cond-mat.dis-nn↗
arXiv1999

Exactly solvable model of inergodic spin glass

A mean-field model of Ising spin glass with the Hamiltonian being a sum of the infinite-range ferromagnetic and random antiferromagnetic interactions is studied. It is shown that this model has phase transition in external magnetic field into inergodic spin glass phase with a number of metastable states. The thermodynamic properties of metastable states are studied at T=0 and near the transition. The relations between the characteristics of slow nonequilibrium processes in spin glass phase (such as hysteresis loop form, thermo-remanent and isothermal remanent magnetizations, field-cooled and zero-field-cooled thermodynamic quantities) and thermodynamic parameters of metastable states are established.

cond-mat.dis-nn↗