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Extension of the Anderson impurity model for finite systems: Band gap control of magnetic moments

We study the spin magnetic moment of a single impurity embedded in a finite-size non-magnetic host exhibiting a band gap. The calculations were performed using a tight-binding model Hamiltonian. The simple criterion for the magnetic to non-magnetic transition as given in the Anderson impurity model breaks down in these cases. We show how the spin magnetic moment of the impurity that normally would be quenched can be restored upon introducing a gap at the Fermi level in the host density of states. The magnitude of the impurity spin magnetic moment scales monotonically with the size of the band gap. This observation even holds for a host material featuring a strongly discretized density of states. Thus, it should be possible to tune the magnetic moment of doped nano-particles by varying their size and thereby their band gap.