  We investigate the effect of quantum confinement on the ferromagnetism of
diluted magnetic semiconductor Ga$_{1-x}$Mn$_x$As using a combination of
tight-binding and density functional methods. We observe strong majority-spin
Mn $d$-As $p$ hybridization, as well as half metallic behavior, down to sizes
as small as 20 \AA in diameter. Below this critical size, the doped holes are
self-trapped by the Mn-sites, signalling both valence and electronic
transitions. Our results imply that magnetically doped III-V nanoparticles will
provide a medium for manipulating the electronic structure of dilute magnetic
semiconductors while conserving the ferromagnetic properties and even enhancing
it in certain size regime.
