First principles calculations of anisotropic magnetoresistance in ferromagnetic nanocontacts

Here we present {\it ab initio} transport calculations of ferromagnetic nanocontacts [1] including the spin-orbit (SO) coupling for the very first time. Due to the SO coupling the conductance of the nanocontact changes with the direction of the magnetization giving rise to the so-called anisotropic magnetoresistance (AMR). We investigate the magnitude of the AMR effect while going from the atomic contact regime (BAMR) [2] to the tunneling regime (TAMR) [3]. Our work is motivated by recent experiments on ferromagnetic nanocontacts [4,5] which report much larger AMR values than those usually obtained for bulk materials in agreement with recent electronic structure calculations of ideal monatomic Ni chains [2].\\ {\bf References:}\\ $[1]$ D. Jacob, J. Fern\'andez-Rossier, and J. J. Palacios, Phys. Rev. B {\bf 71}, 220403(R) (2005).\\ $[2]$ J. Velev et al., Phys. Rev. Lett. {\bf 94}, 127203 (2005).\\ $[3]$ L. Brey, C. Tejedor, and J. Fern\'andez-Rossier, Appl. Phys. Lett. {\bf 85}, 1996 (2004).\\ $[4]$ M. Viret et al., Eur. Phys. J. B {\bf 51}, 1 (2006).\\ $[5]$ K. I. Bolotin and F. Kuemmeth, and D. C. Ralph, Phys. Rev. Lett. {\bf 97}, 127202 (2006).