Random Anisotropy Magnet at Finite Temperature

Abstract We present finite-temperature Monte Carlo studies of a 2D random-anisotropy magnet on lattices containing one million spins. The correlated spin-glass state predicted by analytical theories is reproduced in simulations, as are the field-cooled and zero-field-cooled magnetization curves observed in experiments. The orientations of lattice spins begin to freeze when the temperature is lowered. The freezing transition is due to the energy barriers generated by the random anisotropy rather than due to random interactions in conventional spin-glasses. We describe freezing by introducing the time-dependent spin-glass order parameter $q$ and the spin-melting time $\tau_{M}$ defined via $q=\tau_{M}/t$ above freezing, where t is the time of the experiment represented by the number of Monte Carlo steps.