Magnetic behavior of antiferromagnetic and composite ferro-antiferromagnetic nanoparticles

The Monte Carlo simulation technique has been used to study the magnetic behavior of antiferromagnetic and composite ferro-antiferromagnetic nanoparticles which interact with classical Heisenberg interactions. Our simulations reveal the predominant role of the exchange anisotropy in the magnetic behavior of these particles. In the case of the antiferromagnetic particles, at low temperatures the high coercivity of the particles is attributed to surface exchange field. For a wide temperature range, the coercivity lies on a universal curve where the field is scaled by the ratio of number of spins in the particle to the number of uncompensated spins. In the case of the composite particles, we rind a reversal in the size dependence of the coercivity at low temperatures. The interface anisotropy results in a considerable increase of the coercivity, and in a more rapid fall with temperature.