Magnetic entropy and magnetocalonc effects in nanometer superparamagnetic system

Calculation on magnetic entropy in a nanostructured superparamagnetic system has been carried out by means of both classical statistical thermodynamics and quantum theory. It turns out that there exists an optimal particle size for nanometer superparamagnets at which a maximum change of magnetic entropy is achieved, and that nanometer superparamagnets have an advantage of enhanced magnetocaloric effects over the conventional paramagnets within the wide distribution of particle size of nanometer materials. The enhanced magnetocaloric effects of nanometer superparamagnets revealed by the theoretical calculation mentioned above have been proved experimentally in the investigation of nanocomposite solid of Gd-Y alloy.