  We experimentally study the transport features of electrons in a spin-diode
structure consisting of a single semiconductor quantum dot (QD) weakly coupled
to one nonmagnetic (NM) and one ferromagnetic (FM) lead, in which the QD has an
artificial atomic nature. A Coulomb stability diamond shows asymmetric features
with respect to the polarity of the bias voltage. For the regime of
two-electron tunneling, we find anomalous suppression of the current for both
forward and reverse bias. We discuss possible mechanisms of the anomalous
current suppression in terms of spin blockade via the QD/FM interface at the
ground state of a two-electron QD.
