SPIN POLARIZATION AND MAGNETO-COULOMB OSCILLATIONS IN FERROMAGNETIC SINGLE-ELECTRON DEVICES

magneto-Coulomb oscillation due to the single electron repopulation in duced by external magnetic field, observed in a ferromagnetic single e lectron transistor is examined in various ferromagnetic single electro n devices. In case of double- and triple-junction devices made of Ni a nd Co electrodes, the single electron repopulation always occurs from Ni to Co electrodes with increasing magnetic field, irrespective of th e configurations of the electrodes. The period of the magneto-Coulomb oscillation is proportional to the single electron charging energy. Al l these features are consistently explained by the mechanism that the Zeeman effect induces changes of the Fermi energy of the ferromagnetic metal having a non-zero spin polarizations. Experimentally determined spin polarizations are negative for both Ni and Co and the magnitude is larger for Ni than Co as expected from the calculated hand structur es.