STUDY OF HYSTERESIS PHENOMENA IN ISING-LIKE PSEUDOSPIN SYSTEMS WITH RANDOM LOCAL REVERSAL FIELDS AND RANDOM SPIN-SPIN INTERACTIONS

We study the hysteresis properties of a generalization of the Sherrington-Kirkpatrick spin-glass model, including, in addition to the random spin-spin coupling constants {J(ij)}, a random distribution {h(i)c} of local spin coercive fields, hindering spin flipping. The system evolution is driven by the time-dependent external field H(t). We investigate numerically the behavior as a function of H of the average magnetization per spin, m(H), and of the spin internal field distribution P(h;H). A rich variety of m(H) hysteresis loops is obtained, whose properties are controlled by the parameters of the {J(ij)} and {h(i)c} distribution. It is found that the contributions of {J(ij)} and {h(i)c} to the coercive field of these loops simply add to each other. An approximate Fokker-Planck equation for P(h;H) is derived, which permits one to understand the main features of P(h;H). In particular, it leads to a natural interpretation of the fact, put in evidence by computer simulations, that P(h;H) is, for small h, a linear function of h, whose slope is independent of H and of the {h(i)c} distribution.