Magnetic properties of ferrofluid emulsions: Model of non-interacting droplets

Abstract

Experimental study of the static magnetic properties of ferrofluid emulsions has demonstrated the nonmonotonic field dependence of the emulsion magnetic permeability. In a weak magnetic field, the emulsion permeability rapidly grows and reaches a maximum, and then it decreases slowly in stronger fields. We suggest a theoretical description of the effect based on the following idea. The weak field growth of the emulsion magnetic permeability is caused by the droplet elongation and the resulting reduction of demagnetizing field under the constant value of the ferrofluid magnetic susceptibility. Subsequent decrease of the emulsion magnetic permeability in a stronger magnetic field is explained by the decay of the ferrofluid magnetic susceptibility under an approximately constant degree of droplet elongation.