Correlation effects in small magnetic systems

Computer simulation of the behaviour of a chain of magnetic atoms described in the framework of the extended Ising model has been performed. Non-magnetic impurity atoms were injected into the sample and the formation of magnetic clusters was examined. The simulation of relaxation processes of the transition between magnetic phases was based on the application of the Metropolis algorithm of the Monte Carlo method. Antiferromagnetic material was placed in conditions favourable to the nucleation of ferromagnetic order (parameters were selected on the basis of phase diagrams) and the relaxation time and the size of forming clusters were monitored. The dependence of the correlation length of the magnetics on temperature and sample size was evaluated using the modelling data. An anomalous behaviour of the spin correlation for samples of finite size at low temperatures was found.