Giant magnetoresistance of nanoscale ferromagnetic heterocontacts

The first part of the paper is devoted to theoretical study of magnetoresistance in point nanocontacts between non-identical ferromagnetic metals in the quasiclassical approach. The dependence of magnetoresistance on size of nanocontacts and the electron mean free path is investigated. The thickness of the domain wall in nanocontacts was considered equal to the contact length. The case of a dielectric oxide layer possible presence between contacting metals is also considered. The tunelling magnetoresistance is calculated, and its dependence on the applied voltage and the electron mean free path is studied. The results of calculations agree fairly well with the known experimental data.
In the second part of the paper, the theory of quantized conductance of atomic size nanocontacts is studied in the context of quantum theory of scattering which accounts for reversal of the electron spin. The exact solution of the Schrodinger equation for a particle moving in the linear potential is used as a zero approximation. The difference between the actual potential of domain wall and the linear potential is considered as a perturbation to calculate the spin-conserving and spin-flip conductances of nanocontacts. It is shown for the first time that the conductance with the spin-flip imposes natural constraint on the infinite growth of magnetoresistance upon decreasing the nanocontact size.