On the role of dipolar coupling in the magnetization reversal process in hard-soft nanocomposite magnets

We present simulations of hysteresis curves of simple nanocomposite hard-soft magnets. The coercivity was investigated for triads of hard-soft-hard grains having different magnetization-to-anisotropy ratios m=μ₀M_s² /2K. The systems were described by a micromagnetic model taking into account anisotropy, Zeeman, exchange and dipolar energies and their dynamics were followed by a Monte Carlo Metropolis algorithm. The exchange-to-anisotropy ratio a=Ad^-2/K was assumed large enough to provide good intergrain coupling. Then, for small m values in the hard grain, the propagation of the reversal process into those grains occurred through a Neel-like wall, whereas, for m>0.25, a Bloch-like wall was observed