MONTE-CARLO SIMULATION OF ISING-MODELS WITH DIPOLE INTERACTION

Recently, a new memory effect was found in the metamagnetic domain structure of the diluted Ising antiferromagnet FexMg 1-xCl2 by domain imaging with Faraday contrast. Essential for this effect is the dipole interaction. We use a Monte Carlo method to simulate the low-temperature behavior of diluted Ising antiferromagnets in an external magnetic field. The metamagnetic domain structure occurring due to the dipole interaction is investigated by graphical representation. In the model considered, the antiferromagnetic state is stable for an external magnetic field smaller than a lower boundary Bc1 while for fields larger than an upper boundary Bc2 the system is in the saturated paramagnetic phase, where the spins are ferromagnetically polarized. For magnetic fields in between these two boundaries a mixed phase occurs consisting of ferromagnetic domains in an antiferromagnetic background. The position of these ferromagnetic domains is stored in the system: after a cycle in which the field is first removed and afterwards applied again the domains reappear at their original positions. The reason for this effect can be found in the frozen antiferromagnetic domain state which occurs after removing the field at those areas which have been ferromagnetic in the mixed phase.