Numerical studies of transport properties through point contacts of magnetic metals

We theoretically study the electric transport through atomic-size point contacts of magnetic metals. The conductance in spin-polarized states is examined using Green's function method, considering the electron-electron interaction within the unrestricted Hartree-Fock approximation (Stoner magnetization). In a single band model, the conductance quantization is observed in units of e²/h per spin direction. In a two-band model, in which broad and narrow bands coexist at the Fermi level, the conductance is considerably suppressed by the interband scattering around the point contact when electrons are spin-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. This is in accordance with experimental results using Ni break-junctions.