Theoretical study of the conductance of ferromagnetic atomic-sized contacts

In this work, we study theoretically the conductance of atomic contacts of the ferromagnetic 3d materials Fe, Co, and Ni. For this purpose, we employ a tight-binding model and we focus on the analysis of ideal contact geometries. In agreement with previous theoretical results, the 3d bands of these transition metals play the key role in the electrical conduction of atomic contacts. As a consequence, in the contact regime, there are partially open conductance channels and the conductance of the last plateau is typically above G(0)= 2e(2) . Furthermore, in this regime, there is no complete spin polarization of the current (i.e., both spin bands contribute to transport ) and the amplitude of the conductance as well as its spin polarization are very sensitive to disorder in the contact geometry. Finally, we find that in the tunneling regime, a high spin polarization of the current can be achieved.