Theory and simulation of antiferomagnetic nano-particles

Abstract The structural behavior of ideal, bulk FCC antiferromagnets in a field is known to be very complex (Phys. Rev. Lett. 53 (1984) 1692; Phys. Rev. Lett. 61 (1988) 629, Phys. Rev. Lett. 64 (1990) 1421). Kodoma and Berkowitz (Phys. Rev. B 59 (1999) 6321) found that for example even small NiO particles had a non-colinear structure with several sublattices. This is confirmed by Monte Carlo simulations, which are well suited for studying the temperature and field dependence of magnetic nano-particles. It is further found that during the magnetization reversal in a field a given, complicated tour is taken from the 4- q ground state among various multi- q states. The energy differences between the non-colinear states are small, and they are all populated at room temperature. The relaxation behavior of a simple, ideal system is studied and discussed. It is found that the multi- q ordering in FCC antiferromagnets in a field severely limits the exchange biasing potential since a flipping of the excess moment requires only a flipping of a small fraction of the individual spins.