ballistic conductance of

thin magnetic wires

RENAT F. SABIRIANOV

Department of Physics, University of Nebraska at Omaha

Center for Materials Research and Analysis, University of Nebraska at Lincoln

An electrical conductance of a metallic wire with a diameter of a few atoms has attracted significant attention recently [1, 2]. Because the size of the wire is comparable to the Fermi wavelength of the conducting electrons in metal, the electrons transport ballistically along the wire and form well-defined quantum modes in the transverse direction. Each mode contributes equally to the conductance, thus, the conductance becomes quantized and is given by NG₀, where G₀=2e²/h is the conductance quantum and N is the number of the modes. It has been proposed that such nanowires may be used as conductors and as single-atom digital switches in nanoelectronic circuits. The conductance quantization is sensitive to the adsorption of a molecule onto the nanowire, which may lead to applications in chemical sensors. A low value of the last conductance step was also observed in nanowires and nanocontacts of transition metals having partially occupied s and d states. A minimal conductance step in Ni nanocontact preferentially near 2 and 4 at RT and zero field, near 4 at 770 K and zero field, and near 3 or 1 at RT with an applied magnetic field. [1, 2] We perform ab initio calculations of the electronic structure and conductance of atomic-size Fe, Ni and Co nanowires. We have found several interesting effects. (1) Ballistic conductance may depend on the orientation of applied magnetic field, resulting in ballistic anisotropic magnetoresistance. This effect occurs due to the symmetry dependence of the splitting of degenerate bands in the applied field, which changes the number of bands crossing the Fermi level [3]. (2) We find that the ballistic conductance changes with applied stress. Even for thicker wires the ballistic conductance changes by factor 2 on moderate tensile stain. (3) Magnetic moments in atomic scale domain walls formed in nanoconstrictions and nanowires are softened which affects dramatically the domain wall resistance.

1 H. Oshima and K. Miyano, Appl. Phys. Lett. 73, 2203 (1998).

2.T. Ono, Yu. Ooka, and H. Miyajima, Appl. Phys. Lett. 75, 1622 (1999).

3. J. Velev, R. F. Sabiryanov, S. S. Jaswal, E. Tsymbal, “Ballistic anisotropic magnetoresistance” Phys. Rev. Lett. 94, 127203/1-4 (2005)