Electric transport through atomic-size point contacts of magnetic metals is theoretically studied. The conductance in spin-polarized states is examined, using a Green's function method to take into account the electron-electron interaction. In a single s-band model, the conductance quantization is observed in units of e2/h per spin direction. In a two-band model (broad s and narrow s bands), the conductance is considerably suppressed by the interband scattering around the point contact when the spin is polarized in one direction in the whole system. When the spin polarization on one side of the contact is anti-parallel to that on the other side, the interband scattering is not relevant and the conductance is quantized. These calculated results are in accordance with experimental results for break-junctions of Ni.
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