Effect of magnetic particle chain formation on the entropy change in superparamagnetic nanocomposite systems

A simple numerical simulation model was developed to study the effect of magnetic particle-chain formation on the entropy change of a superparamagnetic nanocomposite system comprised of magnetic and nonmagnetic particles. The random deposition of these particles results in the formation of chains that have the magnetic particles in contact. The number and length distributions of these chains depend on the relationship between the number of magnetic particles and the number of nonmagnetic particles within the composite. These chains increase the equivalent size of the particles resulting in a net decrease in the entropy change of the system. This decrease in the entropy change also depends on the dilution of the composite by nonmagnetic particles. For large particles, dilution increases the entropy change; whereas for small particles, dilution reduces the entropy change. Results from this simple model provide further insight into existing theories on how to enhance the magnetocaloric effect in superparamagnetic nanocomposite systems.