paper

Off-equilibrium scaling behaviors driven by time-dependent external fields in three-dimensional O(N) vector models

arXiv:1512.06201 · doi:10.1103/PhysRevE.93.032141

Abstract

We consider the dynamical off-equilibrium behavior of the three-dimensional O vector model in the presence of a slowly-varying time-dependent spatially-uniform magnetic field , where is a -dimensional constant unit vector, , and is a time scale, at fixed temperature , where corresponds to the continuous order-disorder transition. The dynamic evolutions start from equilibrium configurations at , correspondingly , and end at time with , or vice versa. We show that the magnetization displays an off-equilibrium scaling behavior close to the transition line . It arises from the interplay among the time , the time scale , and the finite size . The scaling behavior can be parametrized in terms of the scaling variables and , where and are appropriate universal exponents, which differ at the critical point and for . In the latter case, and also depend on the shape of the lattice and on the boundary conditions. We present numerical results for the Heisenberg () model under a purely relaxational dynamics. They confirm the predicted off-equilibrium scaling behaviors at and below . We also discuss hysteresis phenomena in round-trip protocols for the time dependence of the external field. We define a scaling function for the hysteresis loop area of the magnetization that can be used to quantify how far the system is from equilibrium.

16 pages, extended text and refs

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