Abstract
We study the prospect of using magnetic nanoparticles for the diluted magnetic semiconductors. The Ruderman-Kittel-Kasuya-Yosida formula is modified by explicitly taking into account the role of the charge carriers inside the nanoparticles in addition to those in the medium. Calculations are done analytically. The final form of the coupling is similar to the original formula, except for an additional phase term which gives a novel oscillatory feature with respect to the particle size, an interesting analogue to the same behavior when we vary their distance. This is to be contrasted with the previous approach which did not include the inner carriers and ended up only favoring a ferromagnetic coupling. The effect of inevitable deviations from a perfect sphere is estimated by the Born approximation. Our derivations can be readily generalized to finite temperatures. © 2009 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA.