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 ( g). Each nanoparticle is described by a pair of exchange-coupled ( J), anisotropic spins ( K C, K S) (Meiklejohn–Bean (MB) model). The magnetization hysteresis loop is obtained using the Metropolis Monte Carlo (MC) algorithm. For magnetically hard nanoparticles ( K C ⩾g) 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.