Quasi-realistic distribution of interaction fields leading to a variant of Ising spin glass model (original) (raw)
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Journal of Magnetism and Magnetic Materials, 2010
In this paper we present an analysis on the hysteretic behaviour of magnetic nanoparticles described by a Random Anisotropy Ising Model. We have carried out an extensive study on the size, kinetics and inter-atomic interactions strength influences on the width and shape of the hysteresis loops of spherical particles composed by atoms situated in a cubic crystalline structure and interacting by the way of magnetostatic and exchange interactions.
Journal of Statistical Mechanics: Theory and Experiment, 2014
We perform equilibrium parallel-tempering simulations of the 3D Ising Edwards-Anderson spin glass in a field. A traditional analysis shows no signs of a phase transition. Yet, we encounter dramatic fluctuations in the behaviour of the model: Averages over all the data only describe the behaviour of a small fraction of it. Therefore we develop a new approach to study the equilibrium behaviour of the system, by classifying the measurements as a function of a conditioning variate. We propose a finite-size scaling analysis based on the probability distribution function of the conditioning variate, which may accelerate the convergence to the thermodynamic limit. In this way, we find a non-trivial spectrum of behaviours, where a part of the measurements behaves as the average, while the majority of them shows signs of scale invariance. As a result, we can estimate the temperature interval where the phase transition in a field ought to lie, if it exists. Although this would-be critical regime is unreachable with present resources, the numerical challenge is finally well posed.
Behavior of Ising Spin Glasses in a Magnetic Field
Physical Review Letters, 2008
We study the existence of a spin-glass phase in a field using Monte Carlo simulations performed along a nontrivial path in the field-temperature plane that must cross any putative de Almeida-Thouless instability line. The method is first tested on the Ising spin glass on a Bethe lattice where the instability line separating the spin glass from the paramagnetic state is also computed analytically. While the instability line is reproduced by our simulations on the mean-field Bethe lattice, no such instability line can be found numerically for the short-range three-dimensional model.
Critical aspects of three-dimensional anisotropic spin-glass models
The European Physical Journal B, 2015
We study the ±J three-dimensional Ising model with a longitudinal anisotropic bond randomness on the simple cubic lattice. The random exchange interaction is applied only in the z direction, whereas in the other two directions, xy -planes, we consider ferromagnetic exchange. By implementing an effective parallel tempering scheme, we outline the phase diagram of the model and compare it to the corresponding isotropic one, as well as to a previously studied anisotropic (transverse) case. We present a detailed finite-size scaling analysis of the ferromagnetic -paramagnetic and spin glass -paramagnetic transition lines, and we also discuss the ferromagnetic -spin glass transition regime. We conclude that the present model shares the same universality classes with the isotropic model, but at the symmetric point has a considerably higher transition temperature from the spin-glass state to the paramagnetic phase. Our data for the ferromagnetic -spin glass transition line are supporting a forward behavior in contrast to the reentrant behavior of the isotropic model.
Field-Driven Hysteresis of the d=3 Ising Spin Glass: Hard-Spin Mean-Field Theory
2008
Hysteresis loops are obtained in the Ising spin-glass phase in d=3, using frustration-conserving hard-spin mean-field theory.[1] The system is driven by a time-dependent random magnetic field HQ that is conjugate to the spin-glass order Q, yielding a field-driven first-order phase transition through the spin-glass phase. The hysteresis loop area A of the Q-HQ curve scales with respect to the sweep rate h of magnetic field as A-A0 ˜ h^b. In the spin-glass and random-bond ferromagnetic phases, the sweep-rate scaling exponent b changes with temperature T, but appears not to change with antiferromagnetic bond concentration p. By contrast, in the pure ferromagnetic phase, b does not depend on T and has a sharply different value than in the two other phases. [1] B. Yücesoy and A.N. Berker, Phys. Rev. B 76, 014417 (2007).
The field-cooled (FC) process on an Ising spin-glass model is investigated by a standard Monte Calro (MC) method on one hand, and the equilibrium magnetization of the same system is evaluated by the exchang MC method on the other hand. The two types of simulation reveal intriguing glassy (nonequilibrium) dynamic properties of the FC magnetization (FCM) of the system. Particularly, the FCM decrease is observed when the FC process is halted at a low temperater, although its value is smaller than the corresponding equilibrium value. We present a comprehensive interpretation of such peculiar phenomena based on the scenario for the FCM process recently propsed by Jönsson and one of us (HT).
Hysteresis and avalanches in the random anisotropy Ising model
Physical Review B, 2001
The behaviour of the Random Anisotropy Ising model at T=0 under local relaxation dynamics is studied. The model includes a dominant ferromagnetic interaction and assumes an infinite anisotropy at each site along local anisotropy axes which are randomly aligned. Two different random distributions of anisotropy axes have been studied. Both are characterized by a parameter that allows control of the degree of disorder in the system. By using numerical simulations we analyze the hysteresis loop properties and characterize the statistical distribution of avalanches occuring during the metastable evolution of the system driven by an external field. A disorder-induced critical point is found in which the hysteresis loop changes from displaying a typical ferromagnetic magnetization jump to a rather smooth loop exhibiting only tiny avalanches. The critical point is characterized by a set of critical exponents, which are consistent with the universal values proposed from the study of other simpler models.
Hysteresis in a dipolar Ising model
Physica B: Condensed Matter, 2000
Zero-temperature Monte Carlo simulations are performed to study the magnetic hysteresis in a three-dimensional model with only dipolar interactions among the Ising spins located inside a sphere on a cubic lattice. Relevant di!erences are found in the site energy distributions between the up and down spins during the magnetization process. Variations of the dipolar energy and the density of incomplete columns are also discussed.
Numerical Study of Competing Spin-Glass and Ferromagnetic Order
Physical Review B - PHYS REV B, 1997
Two and three dimensional random Ising models with a Gaussian distribution of couplings with variance J and non-vanishing mean value J0 are studied using the zero-temperature domain-wall renormalization group (DWRG). The DWRG trajectories in the (J_0,J) plane after rescaling can be collapsed on two curves: one for J_0/J > rc and other for J_0/J < r_c. In the first case the DWRG flows are toward the ferromagnetic fixed point both in two and three dimensions while in the second case flows are towards a paramagnetic fixed point and spin-glass fixed point in two and three dimensions respectively. No evidence for an extra phase is found. Click here for the full text of the paper.
Hysteresis Loops and Phase Diagrams of the Spin-1 Ising Model in a Transverse Crystal Field
Chinese Physics Letters, 2012
Within the framework of the effective-field theory with a probability distribution technique, which accounts for the self spin correlation functions, the ferromagnetic spin-1 Ising model with a transverse crystal field on honeycomb, square and simple cubic lattices is studied. We have investigated the effect of the transverse crystal field on the phase diagrams, magnetization, hysteresis loops and χ z,h of the system. A number of interesting phenomena for the system are discussed.