Magnetic properties of dense nanoparticle arrays with core/shell morphology

Abstract

We calculate the magnetization hysteresis for an ordered array of composite magnetic nanoparticles with a ferromagnetic (FM) core and an antiferromagnetic (AFM) shell, located on a triangular lattice and coupled via magnetostatic forces. Each nanoparticle is described by a pair of exchange-coupled (J), anisotropic spins (Meiklejohn-Bean model). The magnetization hysteresis loop is obtained using the Metropolis Monte Carlo algorithm. For magnetically hard nanoparticles we find that the coercivity is reduced with increasing the dipolar coupling strength, while the exchange bias field shows an non-monotonous behavior resulting from the competition between the random anisotropy and interparticle dipolar interactions. The possibility of enhancing the exchange bias field by increasing the packing density is discussed.