Monte Carlo simulation of a random-field Ising antiferromagnet

Abstract

Phase transitions in the three-dimensional diluted Ising antiferromagnet in an applied magnetic field are analyzed numerically. It is found that random magnetic field in a system with spin concentration below a certain threshold induces a crossover from second-order phase transition to first-order transition to a new phase characterized by a spin-glass ground state and metastable energy states at finite temperatures.

Study of the low-temperature behavior of a disordered antiferromagnet with random fields by the parallel-tempering method

“…The strong decrease in M stg with increasing L at noticeably smaller changes in the spin-glass order parameter indicates the predominance of spin-glass ordering in the system with L > 24 and the appearance, in the low-temperature phase, of a mixed phase state consisting of antiferromagnetic and ferromagnetic domains surrounded by a spin-glass phase. Note that at a temperature T mix = 5.13 the temperature dependence of the total magnetization for the lattice with L = 40 reaches a maximum with a subsequent characteristic decrease in M(T ) in the high-temperature region, as was observed in [13]. The results obtained indicate that, in the limit of L → ∞ and T → 0, a spin-glass ground state is 10 realized in the system.…”

“…In this work, we consider the same antiferromagnetic Ising model (with a spin concentration p = 0.5 corresponding to the region of strong structural disordering) as in [12,13]. The aim is to obtain an additional confirmation of the existence in such systems of a spin-glass ground state and of a complex domain structure by the realization and application, for its numerical study, of the algorithm of the parallel-tempering method which was developed specially for studying the thermodynamics of spin glasses.…”

“…As the examples of the realization of disordered systems with random magnetic fields, uniaxial Ising-like antiferromagnets such as MnF 2 and FeF 2 with impurities of Zn atoms in an external magnetic field can be taken [11]. In [12,13], we for the first time showed, using Monte Carlo computer simulation of the thermodynamic behavior of the disordered antiferromagnetic Ising model with effects of random magnetic fields, that, in weakly disordered systems with a spin concentration higher than the threshold for impurity percolation, a second-order phase transition from the paramagnetic into the antiferromagnetic state is realized. In strongly disordered systems with a spin concentration lower than this threshold value, a first-order transition from the paramagnetic into a mixed state, which is characterized by a complex domain structure consisting of antiferromagnetic and ferromagnetic domains separated by regions of a spinglass phase, occurs in the system.…”

On the nature of the phase transition in the three-dimensional random field Ising model

“…Finally, numerical simulations of the diluted antiferromagnet in a field (DAFF) designed to imitate the random field magnetic systems which are studied experimentally (see below) show that in equilibrium, the transition to the LRO state may be first order [39,40], and moreover it is claimed that at sufficiently strong dilution there is a first-order phase transition to a spin glass state [41].…”

Low-energy excitations in the three-dimensional random-field Ising model

“…Similar to the more prominent spin glasses (SGs) [2,3,4], there are still many open questions concerning the low-temperature properties of the RFIM. During the last few years, the RFIM and the related diluted antiferromagnet in a field have attracted growing attention [5,6,7,8,9,10,11,12,13,14,15,16], in particular within simulation studies at finite [17,18,19,20,21,22,23], and zero temperature [24,25,26,27,28,29,30,31,32,33,34,35,36].…”