  We calculated the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
the magnetic impurities mediated by electrons in nanoribbons. It was shown that
the RKKY interaction is strongly dependent on the width of the nanoribbon and
the transverse positions of the impurities. The transverse confinement of
electrons is responsible for the above size effect of the RKKY interaction. It
provides a potential way to control the RKKY interaction by changing
nanostructure geometry.
