MONTE-CARLO STUDIES OF RANDOM ANISOTROPY MAGNETS

We have carried out systematic studies of the d = 2, n = 2, HPZ model of random magnetic anisotropy, using standard Monte Carlo methods. The non-random, D = 0, case is the usual two-dimensional XY model and exhibits no magnetism or hysteresis at any temperature. We find that at finite D/J (where J is the magnetic exchange) there are significant hysteretic and other irreversible effects. We find, over the Monte Carlo time scales that we run our simulations, four well-delineated regions as a function of temperature: a locked spin glass phase at low T, an intermediate regime in which the spins are correlated to the original directions, a region of algebraic order of the Kosterlitz-Thouless type in which the anisotropy is irrelevant, and a high temperature disordered phase.