  Using a laterally-fabricated quantum-dot (QD) spin-valve device, we
experimentally study the Kondo effect in the electron transport through a
semiconductor QD with an odd number of electrons (N). In a parallel magnetic
configuration of the ferromagnetic electrodes, the Kondo resonance at N = 3
splits clearly without external magnetic fields. With applying magnetic fields
(B), the splitting is gradually reduced, and then the Kondo effect is almost
restored at B = 1.2 T. This means that, in the Kondo regime, an inverse
effective magnetic field of B ~ 1.2 T can be applied to the QD in the parallel
magnetic configuration of the ferromagnetic electrodes.
