Spin-glass surface disorder on the magnetic behaviour of antiferromagnetic small particles

We studied the magnetic properties of an antiferromagnetic small particle of Ising spins. The particle is represented by a two-dimensional array of spins, where the coupling between spins in the core is antiferromagnetic, and its surface is modelled by a shell of spins with competing interactions, simulating a spin-glass type ordering at the surface. We investigated this model by mean-field approximation and Monte Carlo simulations. The magnetic behaviour was studied as a function of the temperature and external magnetic field. Some of the experimental findings observed in real antiferromagnetic nanoparticles, like hysteresis, shifted loops and coercive field, are obtained for this model. We showed that these properties strongly depend on the degree of surface disorder.