Ground states of magnetorheological fluids

Through energy minimization and stability argument, we find the ground states of the magnetorheological fluids to consist of magnetic particles arranged in a body centered tetragonal structure inside spheroidal clusters. The width D of the clusters varies with the length L as D similar to L-n where n = 0.62 for magnetically saturated particles. In the case of magnetically unsaturated particles, the power law variation is divided into two segments, with it = 0.4 in the first segment and n = 0.62 in the large L limit. Our results offer a theoretical framework for the resolution of conflicting experimental observations, with the demagnetization field being the crucial physical consideration.